Transmission is a 4L60E. Truck Starts fine, drives in 1st 2nd, but no 3rd or 4th gears has a high rev, fluid level is near full, but when I put it in drive and go only goes to 40 km ish and sounds like it's in neutral, no clunking, or grinding, or jolting or scraping sounds, reverse and park works fine neutral works too I am stumped should I buy a rebuilt kit new clutches, shift cable and solenoids or shall I start with simplest and go from there