Turbo 400 problems

[Rob 71 chevy]

The guy who built my tranny can't seem to figure this out so I am hoping that someone on this board can. I have had my tranny rebuilt, a turbo 400, a stage 2 shift kit installed with a 2200 stall. My motor is a 350 with a 280 comp cam, if that helps. The electronic shift down is conected to my gas pedal. I believe my rearend is a 3.08. I just got my truck back for the 4th time out of the tranny shop and still problems. If I take off, with it floored, it will shift at 4200 rpms (about 40mph). But, if I am in drive and floor it say at about 2000 rpms, it stays in 1st until I let off the gas. I took it up to 6500 rpms without it shifting. Not good for the motor. I was cruising at 50 mph, about 2500 rpms I believe, and I floored it. The tach went straight to 6500 rpms and it felt llike it went to neutral. I let off the gas and it went back into 3rd. When I am on the freeway at 60mph (about 3200 rpms), and I floor it, it won't shift down at all. I can't get it to shift from 3rd to 2nd, but at lower speeds, going from 2nd or 3rd to 1st ins't a problem, but it doesn't want to leave 1st gear until I let off the gas. This tranny is guaranteed, but I would like to be able to have some answers. I would appreciate any and all advice. Thanks.