5th gear T/C lock up

[boomerkc135r]

I aquired a 02 chev D/A 2500HD Crew cab long bed.
I pull a 12k 5th wheel. When working through the gears to highway speed, 4th gear winds up to about 2600rpm and shifts up to 5th gear and automatically goes into T/C lock up. That drops my rpm to about 1700 and then the engine sounds like it is groaning untill it gets up to about 2000rmp and then runs fine. Should there be a time when it shifts into 5th gear that it should start out in T/C unlock to help get the rpms higher and help you get past the low rpm engine groaning stage. once it gets to 2000rpm it runs great but it really drags at low rpms. This is all new to me so any help will be great.

[Roy W]

Are you using the Tow/Haul mode? As a general rule when in tow/haul, it raises the transmission shift points high enough to keep the engine in the power curve. If you're not using tow/haul with a 12K trailer, you should be. It's actually to your advantage to get the torque converter to lock up, as it reduces transmission operating temperatures.

[boomerkc135r]

I guess my question is, is there a non T/C lockup function on the 5th gear of the 02. Mine will draw down to 50mph and 1500 rpm befor it will shift into 4th gear and the engineis groaning and vibrating all the way down. if it would jump out of T/C lockup and the rpms take a jump of a few hundred I would more than likly have enough power to stay in 5th gear. With the 01 and 02 we dont have the 4th gear on our shift lever so can not down shift manually. How do you like your edge EZ, I am looking at that mod. Thanks.

[oyazi]

Haven't towed that heavy ~ BUT did install an OD (5th)lock-out. It essentially allows one to downshift to 4th. I don't recall the TC lock in 5th as an issue as it seemed eager to downshift to 4th and it becomes unlock way before then.