91 Silverado tranny problem

I hope someone can help me with the transmission problem I 've been having. It all started when I was on a snowmobiling trip and the truck seemed to be revving higher than normal in overdrive, but not as high as if I downshifted to third gear. I also noted the oil was considerably black in color and had an awful odour to it. The truck shifts normal up to highway speed but does'nt seem to lockup properly in overdrive. Is she cooked?

Call www.sonnax.com for help. They will be able to really clear up some confusion for you and get you a solution. They sell all sorts of kits and tranny parts that deal with wierd shifting issues.

The same thing happened to my brother in law's 92., we pulled it and found 4th clutch burned ( and the band). lesson learned, don't use OD, with any load, pulling a grade.