Thanks for your response James in FL. I have checked the forward drive wheels and note there are no Traction Tires or any sign of them being there previously. I do see that there are groves on these wheels. What do I do now?

I received my loco (above) on 21 August 2013. For the first week it ran great, pulling 6 Coal Hoppers & a caboose around the track which has a 3 degree incline in one section. Then it started slipping on the track incline so much it could only pull 4 hoppers with a lot of slipping. My question is:
Are the wheels coated during manufacture with some substance that gives better traction, then wears off after some time of operation?
If this is the case, how can I now reinstate or improve the traction?
As things now stand, the little Loco is not much use on my layout. The Diesels I have pull 12 hoppers with ease.
Thanking you in appreciation,
Richard