my 87 5.7 w/ 700R4 has a subtle problem ... when coasting in 4th gear at speeds from 40-55... w/ foot off the gas the trans seems to disengage like it's in neutral for about a second... then it re-engages into 4th gear again. when it disengages the revs drop to around 900 rpm.
i'm fairly sure it's not dropping down to 3rd when it does this... it feels like the trans is disconnected from the engine when it disengages.

other than that it works great- shifts hard as always and shift points are all fine. checked the linkage and it seems to line up.
any ideas ??
i hope this thing's not about to blow up... i have to drive it from San Diego to canada in a couple weeks.

 

How long before it "re-engages"? The TCC should unlock when you're coasting in 4th with the throttle closing.

 

it takes about 1-2 seconds before it re-engages. the revs seem to drop a lot though...
eg if cruising at 75 kph and 1500 rpm w/ foot off gas it will drop to maybe 1100 when it dis-engages. then right back up to 1500 again when it re-engages 1-2 seconds later.

 

trans problem fixed!! easy fix, no $$ spent. Noice!!! turned out to be the lockup converter was disengaging when it shouldn't ... the problem was the switch which connects to the shifter under the center console . the contacts inside it were dirty... seems to be a common problem w/ older GM vehicles.