you tv valve is sticking in the valve body this is the mosy sensitve part of a 700 r4 I almost never see one that is sticking that you can kleen or replace and fix the problem the trans is coming apart and metal has cause the valve to stick the reason you need the converter to lock-up is that Gm put a orifice in the 4th gear curcuit be cause 99% of the time your in 4th the converter will be locked up when it locked up it makes no heat gm wants it to run at 200 to 280 degrees.when the converter is not locked up it make 99% of all the heat in the trans . you need a trans