I have a 2006 Chevy HHR with the 2.4 and an automatic transmission. I've been servicing it on the severe duty interval, so I had the transmission flushed for the second time about a week ago since it was at 100k miles. Last Tuesday I started getting a P0700 and a P0751, and it will not go into overdrive. When I clear the codes I get first gear back again but when it resets I only have second, third, and reverse. I had a new (and properly programmed) TCM sitting around, so I put it in in hopes of getting things working again. With the new one I again got the first three gears and reverse, but still no overdrive, and when the code set as a P0751 again it was back to second, third, and reverse again. Any advice on a fix for this? Thanks.