I Have A 2001 Super Crew With 92,000 Miles. There Is A 2 Second Delay When Accelerating But More Importantly..in My 4r70 I Feel A Hard Clunk And Hear A Loud Short Squeek When Shifting From 1st To 2nd Gear, There's Also Slight Over-reving. In Addition, My Truck Jerks Simultaneously As If I Had A Manual Racing Transmission Causing Me To Readjust My Rearview Mirror Everytime. I Noticed It At 60,oo Miles But Thought It Was Cool Cause It Felt Like I Was On A Drag Strip. Now I Realize That It's Becoming Worse, Any Advice Or Input Will Do. Thinking About Going To Aamco Transmissions Tommorrow As I Know Ford Dealership Will Rape Me.

 

I'm thinking maybe the squeek may be your belt, mine I believe does it too, and I just replaced it. The clunk could be the splines on your output shaft where the driveshaft slides on (common), and unless you grease it all the time with a teflon, it's there. I also think that clunk has happened to me, only a few times but since I've owned it newer. I can't say, but it seems to happen at WOT, shifting from 1st to 2nd after cruising and then WOT to pass or whatever. It sounds like I broke something, but nothing has ever came about. It kinda sounds like your seat broke a mount or something, hard to describe.