AKMark:
The easiest way to tell if you can just do a flash of TCM for sixth is to look on the drivers side of the trans and if you see the NSBU there then it can't be done. On those transmission that can be done the NSBU is internal.
Denny
Moderator
AKMark:
The easiest way to tell if you can just do a flash of TCM for sixth is to look on the drivers side of the trans and if you see the NSBU there then it can't be done. On those transmission that can be done the NSBU is internal.
Denny
2018 GMC Denali HD 2500 L5P.
Building another 6.2L powered vehicle
Cool that it worked for you. My 05 has the external NSBU, so no 6-speed.
No worries, just figured I'd ask.
05 2500HD CC LB LLY, 4x4, 3.73s 235/85R16's, webasto cab heater, to keep it warm.
03 Buick Rendezvous - When you average over 80 miles per day driving around, you need one of these.
85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
82 K20, 6.2, SM465, NP208, stock except for bed rack, snow plow, and glow plugs are on a toggle switch. It works great for plowing!
72 Postal Jeep - Yet another project
Enthusiast
Inspector,
Will changing the Vin in the ECM cause any problems when getting a smog check?
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A5150nut
2006 K3500 D/A
94 6.5 4x4 5spd Sold
Administrator
Only the TCM is reprogrammed, not the ECM/PCM. The TCM VIN has to be "changed" before the later model calibration will be accepted and installed.Originally Posted by a5150nut
Incidentally, I did my smog inspection today. $57 paid to look for smoke.
Moderator
What D Max said.
Denny
2018 GMC Denali HD 2500 L5P.
Enthusiast
In the earlier Duramaxs you can change the valve body and TCM to convert to a six speed. I've done this to mine some time ago. I just returned from a 2000 mile towing trip, and feel in those circumstances the 6th gear didn't do me any good. I towed mostly in 5th gear.
2004 G.M.C. LLY CC D/A sb 4wd Summit White, ATS Duals, BD X-monitor, BD Exhaust Brake, Snugtop shell, 45 gal. Transferflow fuel tank, AFE stage II
2004 TDI Jetta GLS S/W
2005 TDI Passat GLS S/W
2020 GMC Denali 2500HD
Enthusiast
This is interesting. Haven't read anything about it in a long time, and never have read, before, a report from anyone who had done it.
What is the size and weight of your trailer? And, is it still a $2000~ proposition?
2008 Jaco Seneca 35' motor home (Kodiak 5500 chassis). Pulling 18' Wells Cargo enclosed trailer, with 2016 Miata in it.
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