The tranny, when leaving from a stop (ie; stop sign or light), has begun not engaging in drive, like you're in neutral. The tranny engages going to 1st drive then into hi drive when moving, or by revving the engine slightly and it goes into drive with a jolt (like you've been rear ended)and is fine till, I assume, the hi drive valve free's itself so the gear works.
I thought a stuck valve (varnish?)and put Sea Foam tranny conditioner in the tranny a couple hundred miles ago and now it just seems to happen after high speed driving (heat related? Foaming?.)

After being parked awhile, motor off and cooling down, the car's fine again(tranny cool) until I've driven awhile and it again sometimes has the delay and jolt trying to move from a standing start.
Fluid level is good.

The faq doesn't address this in quite my circumstance that I see.
Any idea what's up?
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steve m