mxzr2
New member
Hi, I'm new to this forum and I need some help. I am a proud owner of a 99 Sierra SLT Z71 5.3 liter extended cab with 270,000 miles. I recently had the motor replaced because my truck had a cracked head and coolant was getting in the oil and it looked like the pudding my kids eat. I replaced the motor with a Class 1 Jasper engine that has a RV cam and its suppose to put out a little more hp. I got the truck back and now it hesitates during acceleration and it downshifts on every hill I come to especially on the freeway. The mechanic replaced the MAF sensor and updated the ECU. I recently had new cats put on and seemed to help, but the truck still hestiates. The new motor only has 4000 mile and it starts and idles fine, just during acceleration and hills is where it struggles. Has anyone had this problem with their truck or does anyone have an idea of what the problem could be?