I have a 2010 Sierra that came factory with a 4.8-4l60e. Installed a l96 6.0 with stage 1 tsp cam kit with a billet 2600 converter. The transmission shifted fine with 4.8 but would not hold in 2nd with the 6.0. I turned torque management way up now it doesn?t slip. Should I rebuild the 4l60 with stronger parts or get a 4l80? The stock transmission has internal prndl. I can?t find an adapter harness.