I've got some 700R4 issues

[birdistheword]

So I have a Stage 3 Raptor 700R4 transmission I put in my 72 K10 and as soon as it shifts to 4th it instantly locks up and bogs down the engine. At highway speeds the engine surges as it locks and unlocks. I have the TCI vacuum switch and newer brake light switch with the 4 terminals hooked up for the lock up converter. I'm kinda stumped and not sure what to do next. Oh and you can't feel the 1-2 shift but the 2-3 shift has a good kick and same for when it downshifts. Any help is greatly appreciated.