2019 Ram 1500 5.7l hemi new body style. I put 6" lift and 35" tires with aftermarket 20's. Looks damn good but I am having issues with a small shake and feels like rear end. I've spoke with a mechanic buddy and 1st thing he asked was if the speedo was reprogrammed after lift for the bigger tires. I don't believe it was done because when I hit school zones my speedo says 20mph but the sign telling how fast your going says 3mph faster than what I'm actually going...and I've gone past many different speed signs and all are 3mph over what my speedo says. Buddy says since it wasn't done, the transmission doesn't know when to shift properly and that could be causing the shaking. I have noticed rpms are a tad higher than before lift was put on before it will shift into next gear. Anyone had this issue before or anyone agree with what my mechanic buddy is saying? Thanks for any help!