35 mph WOT power loss

In all your crawling under, have you disconnected the lever at the transmission to see if it can go back any farther? I know I keep hammerin on it, but it's that important. If all you're doing is just crawling under and trying to push the lever back, you may be missing it. Unless you disconnect the lever at the transmission, you're not eliminating "all the rest" from holding the throttle lever a little forward. You need to isolate that lever and make sure it has FULL TRAVEL rearward. You could save yourself pulling the pan.