Thanks for the effort you've put in to helping me solve this mystery.
I'll take some time to digest and then try your recommendations and let you know the results.  In the meantime I'll carry on with my much needed work on the landscaping.  Time to get some ballast on the track for starters.

So, the good news is that I believe the mystery has been partly solved.

I took your advice about checking the voltage across the rails and found no problems there either in the DC or the DCC mode.  Given that the voltage reading increased as I increased the throttle reading as it should, I then decided to try putting the engine back on the track.  With the controller in the DC mode the engine ran in both directions in the small portion of the track I uncovered (about 10") to do the voltage testing. With the controller in the DCC mode it only ran backwards. Apparently I had only tested the engine in the DCC mode since that was my goal for future operations. HOWEVER  I repeated the engine on the track test the next day and got the opposite results.  With the controller in the DCC mode the engine ran in both directions but only ran backwards in the DC mode.
At this point I'm happy that in one of the two modes it will run in both directions.  I only have one train running at the moment and it will be a while before I add another.
I'm thinking at this point it may be the decoder in the engine. Not sure what the next step should be short of replacing the decoder. 
Would temperature have any effect on operation?  My garage is in the low 40s until I turn the heat on and then it only gets into the low 50s.  I know that the temperature was about 40 for the last test I did.

Thanks for the quick reply.
I purchased the engine (both A & B units) new from a hobby shop in Columbus, OH about 3 years ago.
I have a volt meter.  I haven't used it on the tracks yet but will use your directions to have a go at it.  I hope to get back to it shortly.  Right now all track is covered with tape because I've been using Sculptamold and plaster sheets to do some landscaping.  Can I uncover just a portion of the track to test it?

Thank you so much for taking a stab at solving my problem.  I was concerned that this was going to remain a mystery and I was either going to need to purchase a new engine or invest in a DCC only controller.  Here are answers to your questions:
The engine has a decoder but not for sound.
It will run on either DC or DCC.
If I place the engine on the track with the nose heading to the left, it only runs left to right, ie. backwards.
If I turn the engine 180 degrees and have the nose heading to the right, it only runs right to left, ie. backwards.
Regardless of the direction pressed on the controller, the engine runs backwards.

You did a good job translating my initial explanation.
I hope this provides you with enough to venture a guess at what I've missed.  I spoke with someone at Walther who runs N Scale and in the end he thought the controller may be sending a DCC signal but that the decoder might be translating it to DC somehow.  If this was the case then there might be a compatability issue. I hope a strictly DCC controller is not the problem. My budget would be squeezed if I need to spend $200+ on a controller and have the Tech 6 gather dust.

Thanks again for pitching in.

I am relatively new to model railroading and may have made a rookie mistake somewhere along the line before I placed my engine on the track.
Some detail may help someone provide me with what I hope is a very simple answer to my problem which is that regardless of which direction I place the engine onto the rails, it only runs backwards.
About 3 years ago I built an N scale layout with a total of about 27' of flexible rail.  I soldered 20-gauge feeder wires to the track at approximately 4-5' intervals.  I connected the feeder wires to a 12 gauge wire bus which I have connected to an MRC Tech 6 Sound Controller 2.0  All of the outer feeder wires are connected to one of the bus wires and all of the inner feeder wires are connected to the other.  There are 5 turnouts and 5 terminal ends included on the layout.  About 2 years ago, once I had all the track and wiring in place, I put my new Bachman diesel model 3274 on the track.  While the performance was not spectacular, I do not recall that it only ran backwards. 
For reasons I will not go into here I was unable to do any further work on my setup until this past December.  After a light cleaning of the track with a Bright Boy and minor housekeeping I once again wanted to see my train run before I ballasted the track and began any serious landscaping.  It was at this point that regardless of my best efforts I could not get the engine to run forward.  I have done some preliminary searching for an answer on the internet without success.  The closest I've come is several comments advising that there is a switch or wires on the engine motor that need to be reversed.  I hesitate to do something unnecessary and am reluctant to begin taking the engine apart if the problem is in the track wiring or somewhere else more easily accessible.  I live in a town that has no organized model railroading clubs or any stores with people knowledgeable about model railroad wiring or other aspects of the hobby so at the moment I'm at a loss for help nearby. I hope to locate some local help soon but would appreciate any help in the meantime.