Cummins starts in overdrive
 

Hey guys i just got my cummins. Its a 95 12v. When i start the truck up and put it in gear it starts off in overdrive and wont come out of overdrive until i hit 40 or 50mph. Is it bad for the trans to be started off in low speeds in OD. Any advice on how to fix this or anything would be appreciated

What you're saying does not make sense. First of all, the truck doesn't have the balls to take off in OD, and 40-50 is where it would go into OD, not come out of it. OD on is the default setting for the trans when you start it, but 1-2-3 are the same whether OD is on or off. Regardless, I think you should clarify what exactly it is you think is happening, because either there is something very wrong with your truck, or you're confused.

If you're concerned about it, put it in 1st to take off and then upshift it manually. Unlike first gear in the Drive position, 1st gear in 1st position engages every drum in the trans including the reverse drum, making it the strongest gear- but you'll have to shift out of 1st eventually.