4l60e in my 2000 rcsb with a whipple 😜. Come up to a stop sign, it turns green, u take off and it revs up about 200 rpm and then just engages. It does it in OD,D, and 2 but not in low or 1st manually. Line pressure is 65+. So what ya think a guy should look at first?
Yes fluid is good.

 

Is this a riddle? Stop signs don't change colors....

 

Lights... My bad.

 

In could be that the low roller clutch is not holding. When putting the trans in low the low/reverse clutches are applied, overriding the low roller clutch.

What is a rcsb?

 

Regular cab short box. Well that suxs.. That's internals.

 

If the issue stops in manual low the only thing that I can think of that changes when in manual low is that the low/reverse clutches come on and override the roller clutch. The low roller clutch is a mechanical clutch that looks something like a roller bearing but will only turn in one direction. Yes it is an internal part.

 

This sounds like a high stall speed torque converter to
me. What's the problem? That you don't (think you)
have one?

 

I assume the OP is stating that this problem just started happening. And that "just engages" means its suddenly grabs and not a gradual process as with a high stall converter.

OP: This is why a more detailed description is needed for us to reach the most likely diagnosis.

 

No stall. No it ls not gradual, been doing it for awhile, in drive on flat ground with the brake off it won't roll forward until u give it 2-300 rpm. Then just takes off.

 

In this case I'd begin with fluid level; last TC swap, I
got the car back with about 3 quarts short and it kind
of behaved this way. Marginal pickup at the pump.