is this a srt6 or limited ,, find someone near you that has a crossfire if yours is limited then limited and put his tcu into your car if it is a gear ratio problem then this will solve it. then you get a tcu or yours retuned
these trannys don't go bad unless abused or run with no fluid. i don't think it is the tranny
there is the Kansas city crossfire group ( on here https://www.crossfireforum.org/forum...ht=kansas+city maybe one of them can help. for now don't get the tranny rebuilt.