Tony - I fully intend to put the plastic diffs in the car to see if the IRS outdrives are the problem. However I don't see how the spur gear adapter could be causing anything, I will replace that with the stock part also if you recommend it.
The problem here is that the plastic diffs melt when running mod. When I got my TC3 I melted the diff every run no matter what I did to the car, until I got the IRS outdrives. Unless you are telling me something is different about the diffs...however they look exactly the same as on the TC3 to me. $120 worth of IRS aluminum parts after buying the FT TC3, I was actually able to FINISH a race without a diff melting.
Josh