First Post, Trans Help

[zen garage]

First post and I need some help. I have an 05 H2, 28k miles, Magnussen S/C, 2800 Yank Torque, headers, exhaust, 4.10 rear and more. Its a pretty built up rig. In the last week or two my trans has been real slow shifting from first to second and second to third. I brought it in to the dealer, they couldnt pull any codes and said it might be my programmer. I reloaded the superchip program and it is still shifting slow. I also spoke with Yank and they said it was a trans issue.

Any thoughts? Similar problems?