A few years ago I built a 63 Monterey for a friend. Now, after what seemed like minor maintenance repairs down the line and the transmission is giving us some trouble. When I owned it I replaced the tired 390 with a fresh built 30 over one and tossed the Cruise-o-matic in favor for the c6. Because the car was built to be as low as possible I had raised the trans tunnel and built new crossmembers, but I've always had issues saving the transmission pan from rocks and debris at a low cruise height. After the last trans pan swap from a 60's econoline the trans doesn't want to kick in gear from 2nd to 3rd. Mind you it will at 1/4 throttle or even 1/2, but at all out full throttle, it stays stuck in 2nd.. Is this an issue from the ultra slim pan added and not enough fluid? I have checked the diaphragm in the back as well as any kinks in lines, but all seems well.Or no enough room between the pan and pick up? I'm at a loss at this point, so any suggestions would be apprecated!