I got a 96 dodge ram 2500 v10 it won't stay in overdrive keeps going back to 3rd gear.

SOURCE: automatic transmission not shifting into 3rd or 4th

my 1999 f250 super duty will not shift into overdrive

SOURCE: dodge ram 3500 won't shift into overdrive

it may of fried your powertrain control modual "PCM"

SOURCE: 96 chevy blazer 3rd gear and overdrive slipping

i got a 1996 chev. blazer s-s10 4.3 engine 4x4.problem i got is i got 1st 2nd & overdrive & reverse but no 3rd gear what should i do

SOURCE: 2001 dodge ram 2500 v10 oil pressure drops to 0 then back up

you need to put an oil pressure gauge on it and see what happens.what you will find is that the sender unit is no good.

SOURCE: 1996 dodge ram 2500 auto transmission not shifting properly

Well, first do the service. Pull the pan down and look for metal shavings. If there is metal shavings your in for a transmission. If not, you may have a problem with one of the transmissions shift solenoids located near the valve body.
P.S. The Duramax has the Allison 1000 transmission not the dodge cummins and they are one of the best trannys on the market.