Moderator
5speed to a 6speed
I went and did it. I just had my 1000MH 5 speed trans TCM reprogramed to allow the 6th speed turned on. I am stoked. After the procedure we put it on the freeway and counted the shifts. They were all there and 6th dropped 400 RPM. 5th at 65 was 2350 and now it's 1950. Nice smooth shifts. Hopefully some milage increases will come along with the reprogram. We are going to drive to Florida in Feb so we'll see.
Denny
2018 GMC Denali HD 2500 L5P.
Building another 6.2L powered vehicle
Interesting, what did you have to do to turn it on?
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
Moderator
Being an 06 I had to have a Vin # of a medium duty that had an active 6 speed. Those vins would be from a mid year 07 to present. The vin # that I used was from an 08. I found a tech that had a GM diagnostic tool called a Tech II and he hooked into the OBDII port and selected the TCM in the truck and replaced my vin # stored there with the vin of the 08. It took about 10 minutes to replace the tables and activate the dormant sixth speed. In 06 all the pickups got the 6 speed but it wasn't until mid 07 that the medium duties got it. Most probably 05s and before won't have the capability to be reprogrammed just with the TCM but can have the valve body and solenoid rail replaced along with a programmed TCM of the 4th generation series installed and then your set albeit at some expense. Good luck
Denny
2018 GMC Denali HD 2500 L5P.
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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-Patrick Henry
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.
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