Put the TPS sensor on it, didnt fix it. Fluid is in the area it should be when its hot. Thats usually when I check it. Its the stock stall speed as the converter that came out of it. Nothing fancy. Talked to the guy who built it for me, we are gonna look at it Tues. Its busting loose pretty bad at 4500 rpm then it hits the rev. limiter. Its pretty bad compared to what it was about a week ago. So we will wait and see, fluid looks fine and doesn't smell burnt, drives like a dream till you floor it and about 4500 it goes to HE**

 

This is still only in third gear right, before shifting to 4th? If so I still say it is internal, either the 3/4 clutches were not tight enough (too much slack) causing early 3/4 clutch wear (but I doubt it if you say the fluid look fine), or one of the hard parts broke (drum, piston, etc.)...

But hey you could be lucky and just have a bad seal that is allowing pressure to bleed off, but that too would cause early clutch wear and you would see and smell it in the fluid...

Anyway, good luck with it, and hope everything works out for you...

 

Hahahah these 4l60es are so bad, mine did the same thing, not sure about 3-4 shift though but 1-2 and 2-3 definetly did it at wot so i just put a another stock tranny in for 25 bucks and no problems since last summer...... let me know what ya find is wrong with yours