I have a 95 B2500 van that I am having a problem with. When driving locally my trans works perfect, if I get in traffic for a while the rest of the time I drive it as soon as I lift off the gas completely it drops out of overdrive at any speed. I think this is heat related, the trans was rebuilt last year and has a cooler installed. I just had a radiator put in and now I show a 35 code. Could these be related? Any help is appreciated.

 

With the engine off try and spin your radiator fan. Does it spin freely or does it have resistance?