97 Van with 7.3 diesel tranny shifting too soon

[swoop]

I have a 97 Ford E350 with the 7.3 diesel with a 4x4 conversion done. The tranny I believe is the E40D with a bolt on transfer case. I'm having a probelm where going up hill/mountain the tranny seems to shift way too soon. Shifts from 2nd to 3rd before it should and the same with 3rd to 4th. The van is not towing anything. Then the other day we were driving up a very steep mountain road and I had to manually shift the shifter to 2nd to get the tranny to climb. Then when it leveled off I shifted the van back to drive. At that point the tranny was stuck in 2nd. I let off the accelerator pedal and the van shifted up to 3rd and eventually to 4th (OD).

A friend stated this is a problem with the accumulator/valve body and I should replace it. I talked to a couple other tranny shops yesterday and I told them the speedometer is off by 5-8 mph due to the tire size (285/75/16). I think the stock tire is a 245. Three tranny shops told me I have a problem with the tire size and that I need to recalibrate the speedometer or adjust the speed sensors.

I purchased a new Edge Evolution yesterday because the shop said I can enter in the tire size and fix my speedometer issue.

Please help, what is my problem or what could the problems be? And can I fix my speedometer due to the tire size with this Edge Evolution. I read through the entire manual and did not find anything regarding tire size and adjusting the speedometer.

Just connected the Edge Evolution to the van and it gave me the following two codes: P1391 and P1393. Searching to see what they mean. I also have a problem with starting the van. Harder than heck to start. But if I plug it in for 1/2 hour or so it starts right up.

Thanks in advanced!