As some of you know, I recently bought my 1998 C2500 knowing it needed transmission work.( it would stall when you put it in reverse like it was going into drive and reverse at the same time) I had the transmission rebuilt including having the valve body replaced as it appears some one had drilled the old valve body to boost shift pressure. The transmission seems to shift fine although it will not shift into fourth until it reaches approximately 48 MPH. I assume this is normal? I have driven it for three or four weeks now and I have noticed that the TCC is not going into lock-up. I read on an earlier post that some trucks will not go into lock-up until operating temps come up.? I have noted that my temp never goes above 170. Could this be the issue? Also I am getting no check engine light codes. Will continued driving with out TCC lock-up do any harm to my transmission or will the fuel mileage just suffer? (I'm getting about 17.8 MPG).