MAN I GOT UP EARLY TO GET MY FLOS PUT ON DUALS COMIN OUT BEHIND EACH TIRE LOOKS GREAT PULL OUT RUN SOUNDIN GREAT GO TO AZ GRAB SOME ITEMS U KNOW START MY WAY HOME TRUCK STARTS JERKIN LIKE IT WANTS TO STALL GET STARTED MESSIN WITH THE TB BECAUSE IT WAS SOUNDING LIKE IT WAS SUCKIN AIR REALLY LOUD CUT THE TRUK OFF STATED BACK SOUND WENT AWAY PUT IN DRIVE IT SLAMS IN TO GEAR LIKE THE IDLES TO AND WHEN I DRIVE IN D IT WONT SHIFT I CAN MANUALLY SHIFT FROM 1 TO 2 BUT NO 2 TO 3 HELP
A automobile is a lot like a human being. When you have a problem, you have to take it to a doctor that can diagnose the problem and find a cure for your problems. Until you know all the particulars, blood pressure, pulse, resperation, and do tests, there is no way to give anything more then a guess.
Let's say they took the cross member off the truck. Let's say that they took the transmission lines off the transmission. Let's say that they crossed the transmission lines when they put them back on. Maybe that would cause a problem.
Let's say that maybe there was a electric shift module and they disconnected one of the wires or one of the wires leaned against a hot exhaust that was not there before - but is there now. Maybe it shorted something out and now the transmission cannot function as well as it coudl before.
Some of these performace upgrades are nothing more then something to make a honest person part with their money. They might look cool or they might sound cool, but if they are not designed properly, they can cost you thousands of dollars to repair when something goes wrong. Just because someone works in a muffler shop, doesn't mean that they are certified mechanic's or that they know what they are doing when it comes to mechanical repairs and they might could have done something wrong.
First stop, take it back to a muffler shop. Second stop, take it to a transmission shop.