Transmission will hesitates when in drive and cold

[newbluehair]

I have a problem. I have a 98 F150 4x4 with the 4R70W tranny. The transmission has been rebuilt 2 years ago, with a present milage to date @ 150000 miles(total). I had engine troubles so I replaces the 4.2L engine and while I was in there replaced the front pump seal ( torque converter seal ). That lasted 4.5 miles and the seal popped out and dumped enough fluid that the tranny beagn to slip. The truck was towed back home and the seal replaced again, this time the seal was loctited in. A new tranny filter and some new merc V and off we go.... But it developed a new issue after 300 miles. Now when the tranny is cold it works fine in reverse, but when drive is selected it acts like it is in neutral while the engine revs up, and them BAM it is taking off just like you revved up the engine and then dropped it into gear. When the tranny warms up this issue goes away. Also when it is cold and acting up, if you select 2nd gear or first it behaves completly normal. When the issue was first noted I tried to drive the truck up on ramps and it would go part way and then roll down again like I selected neutral again. The fluid level is up and all recently added fluid is Quaker State Merc V. I have no reservations about pulling the valve body, I am just going blind here right now. Please help.

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