i am working on an 86 with a 700r4 and305. it shifts fine but when it goes into 4th the t.c. immediately locks up. and the rpms drop WAY down. this is at about 40-45 under normal accel. you either have to touch the brake to unlock it to get more speed or mash it until it goes back to 3rd. my bowtie does not have that drastic drop in rpm's like this one does and i have never had any other vehicle with an auto.

any advice? tv cable,lock-up switch?

i would check the pressures but we are in the middle of an ice storm and i do not have a garage

 

I would check the fluid, make sure that is proper level and good condition (aka does not smell burnt or unknown last change date). If the fluid is good I would readjust the TV cable and try again. I'll be honest I dont know much about the torque converter lockup functions, but those two things are always good to do when the 700 is acting weird.