RPM's drop serveral times when shifting
Hi everyone. I have a 99 F-250 powerstroke and my issue is that the RPM's "bounce" down when it shifts into third and fourth gear. They will drop by 100 or 200 rpm increments to where they should "normally" be when it shifts. It doesn't do it all the time but it seems like the more gas you give it the worse it will be. The truck has been doing this for awhile, and it seems to be worse in the higher settings I put my programmer on. I had the transmission rebuilt less than 3000 miles ago, but this issue was occurring before the rebuild. I took it back to the shop that rebuilt the transmission, thinking it was a transmission issue. He drove it with his computer plugged in and he said it was not a problem with the transmission, but a problem with the motor. Does anyone have any idea what the problem may be or where to start?
Thanks for any help.