I recently purchased a 2WD 99 C1500 Suburban with a 5.7L, 4L60e, and 3.73 rears. It has about 137,000 on it and it appears to be very well maintained. The previous owner told me that it pretty much gets 14 hwy or city. I figured it should have got a little better on the highway. Some friends of mine are claiming high as 19 in theirs. A recent family vacation from east Texas to the Florida panhandle proved the horribly consistent 14 mpg. I actually got as high as 14.2. While in Florida, it developed a very hard 1-2 shift and the CEL came on. When I got back to Texas, I hooked my scanner up and got a P1870 I think it was. Anyways, wound up putting a reman valve body in and now everything is shifting fine, torque converter locking up and it cruises 70 at 2000 rpms. I haven't got to drive it enough to determine the mpg's yet. About how bad does the torque converter not locking up affect the mpg?