I just done a engine swap and have had a lot of issues. It is a 2018 L83 and a 6L80e swapping into a 97 k1500. I have finally got the DTC's clear and current issue is it idles fine but when I put it into reverse or drive it reves really high and then when it engages gear it reves up and down . When I shift back to park or shift to neutral it idles normal. I have not driven it at all but I jacked it up and when my foot is on the brake it does the reving up and down but when I release the brake it seems to spin the tires fine and the idle seems normal and the transmission seems fine I thought it was the transmission for awhile. I can't seem to find anywhere anyone has had this issue, it seems like if the motor is under load it does the reving up and down. I don't know if its something I missed doing with the swap or if its a setting or wiring issue, but it seems odd that it does it only when hifted into gear. I will attach a scan, but im hopeful someone has had this issue and can help me out.