i have a 2000 silverado 1500 5.3 and ive been having problems with performance. sometimes when i give it alot of gas, the truck doesnt want to downshift and takeoff, but it would seem like it accelerates slower then it should, i dont want to say it boggs but rpms dont go up but 2500-3000 rpms because the tranny doesnt want to downshift

any suggestions on what might be the problem?