E350 transmission problem

[Mister Moe]

New member and new to a 98 350 diesel with about 120k on it. Looks like this van was used pretty hard in its former life. I didn't notice this on the test drive but now the o/d light on the shift stalk is flashing - only when in park. The van pulls fine on acceleration but when I let off the accelerator, it slows down quickly. If I just give it a little pedal, it can go into a bucking motion (typically when going downhill). I need to give it a bit more pedal to get it out of this bucking mode. With constant power input at travelling speeds, it's fine again.

I tried to pull codes with a basic code reader but all I got is "no codes". If possbile, I would like work through this problem myself but as a final resort, I'll take it to a trans shop. Any ideas/suggestions?

Also - I checked the fluid, level is good, fluid is red, looks ok, doesn't smell burnt.

Moe

[Mister Moe]

Today I had Autozone scan for codes with their more advanced scanner - no codes. Nothing in memory. As I said, the trans shifts fine on acceleration, it's just deceleration where there seems to be a problem. Maybe it's not the transmission? I did notice that there is a coat hanger wire wrapped around what I think is the turbo wastegate. I did order some manuals but until I receive them, I'm working blind.