I have an 04 Z-71 with very little done to it. Just exhaust. The last few days, the truck has been shifting funny from 1st to 2nd. Every other gear feels fine. It feels like its shifting a little slow then very solid. Sometimes it feels like it doesn't want to go down to first at a stop. No codes yet. Not a serious issue yet, but i'd like to take care of it before it becomes one. Any suggestions? Tranny flush? Additives? Only has 54,000 miles on it