What do you guys think?

Hey guys I have recently gotten my valiant on the road again after replacing a host of things including the trans and rear dif.
So I picked up a low mile 904 and stuck a TF2 kit in it. I know I payed strict attention to the instructions and read them several times before attempting and then several times prior to each step. This leads me to believe I didnt damage the trans my self.
Here is what is going on.
I took the car onto the interstate for the first time since the new trans install and all was going well as I accelerated through the on ramp and merged with traffic. The trans shifted just fine as I let it shift on its own, but I noticed something was screwy, I was well into 3rd gear and it felt like the brakes were dragging, because the car felt as if it was working harder than normal to move. As I continued on, the feeling disapeered fairly quickly. I felt this only one more time as I left a parking lot that same day, this time the speed would have been much slower. It acted the same though.

Now the other thing I have added was an 8 3/4 sure grip rear. Ill be honest I dont know enough about the rear to diagnose whether it may be the rear or the trans. Any ideas?

Oh and when I put the rear in I of course put new lube in it and I added a bottle of "posi" addidtive. Hope that was ok! Hate to have messed this rear up! For some reason as I write this Im beginning to think it may be the rear! Damn!:angry7: