Great, thanks for the info. I may just replace the servo as long as I've got everything apart to replace parts and change from grease to oil. I mainly use my truck just for bashing. My LHS just built a new track so I may take it there and give that a try.

How much oil do you put in the differentials?

Do you have a part number for the servo you ran? And is it compatible with the factory Airtronics radio?

-Is it this one JRPSZ8550? Cheapest I could find it was $97. Does that sound right?
-How about the Hitec HSC-5998TG? Would that also be a good replacement?

I've noticed that when I apply full power that one front wheel or the other picks up off the ground and it pulls to that side. From what you said that sounds like the diffs are unloading.