GMC Repair: 1997 sierra 2500 ecm swap question, gmc dealer, alpha numeric

Question
QUESTION: My Truck has been running bad lately.  It will idle and accelerate well, but when you ease off of the gas to maintain speed it will start acting up by popping and hopping.  I toke the truck to a GMC dealer and they said that the ecm would not talk to their computer at all.  So, I figured the ecm was the cause of the problem.  I found an ecm from a 97 1500 the letter codes were almost the same (mine-BNHR, other one-BNHP).  When I installed the new computer it started up and ran well, but it is shooting PO740 and PO785 codes at me and it will not go at all.  When  I give in gas while in gear it bogs down and goes no where.  Is this due to the new ecm having a program for a different transmission?  Can this be re programed?  Or do I need to get a different ecm?

Thanks for your help,
Jody

ANSWER: Hi
It will need to be programmed.
Those codes are Transmission codes.

Was the Engine size the same? Does your vehicle have a 4L80E tranny? Or a 4L60E. That is COULD BE your problem.
The PCM will need to be re programmed at a dealership.
Good Luck
Hope this helps
JUST advice from experience.
Pawl


---------- FOLLOW-UP ----------

QUESTION: I'm not sure which transmission that it has.  Can you look at them and tell them apart?  Can anyone else program it or just the dealers?  I am thinking about sending the ecm to someone to program the maps to give me better performance.  Can these people also re-program the transmission settings?

Answer
Hi
In the glove box, you should have a sticker with the RPO codes for your truck. It'll be about 3"x3" sticker with ALOT of alpha-numeric 3 digit codes.
Look for one that is M30. If you have M30 you have a 4l60E tranny.
I don't know the code for the 4L80E codes. But I will say if you physically look at the tranny pan, the 4L60 is fairly square shape. May not be an exact square, but at just a glance it'll look close.
The 4L80 is more rectangular and MUCH deeper pan. You'll see it just LOOKS big.
As far as Reprogramming, alot of independent shops have the ability to reprogram GM PCM's. USUALLY any that are ACDelco certified will have capability. Check around, it is a fee that a shop must pay, but it will not be that hard to find one, I think. Check around, but please make sure they know what you have done. Tell them you got the used PCM. Some shops MAY NOT want to mess with it. I'll be honest, but I'm sure you'll be able to find one.
The send out, I PERSONALLY, am not a huge fan of this practice. However, I understand the wheres and whys, so I don't tell folks not to do it. I am not all that familiar with the process, but I am sure they can tweak the tranny settings (eg shift points, line pressures, etc..). I would think you could enquire them and see what they can and cannot do. Again, tell them whats been done, or what YOU want the truck to do. I do know the Reprogrammers you can buy at parts store USED to cause tranny problems. They would alter certian resistnces it the PCM data checks and codes would set and they were NIGHTMARES to diagnose. That was a few years back, so they have certainaly (I Hope) fixed these problems.
Anyways, Jody, I hope my rambling on helps.
Please if you need other assistance, don't hesitate to post back.
Keep me informed.
Pawl