Engine trans swap/replacement

My tahoe has 220k on the stock drivetrain, the engine (LMG) has never been AFM deleted, still works fine apart from having a rough idle and P015b&d that I cant get rid of, and some oil consumption. My old 6L80 is starting to feel like it needs a rebuild and is making a weird rattling sound when cold. With that being said I’m starting to look at options before something fails on me. I would love some input on the following:

-Possible L33 longblock swap (about 100lbs lighter than the iron block LMG and a little more power), wanting to know if everything from the electronics of the LMG will work with it.
-Possible 6L90 swap, might as well upgrade if I’m going to change the trans, but what is required to swap since I believe it is 1 in longer than the 6L80, and would it be worth it?

Thanks in advance!

JkTahoe1 said:

My tahoe has 220k on the stock drivetrain, the engine (LMG) has never been AFM deleted, still works fine apart from having a rough idle and P015b&d that I cant get rid of, and some oil consumption. My old 6L80 is starting to feel like it needs a rebuild and is making a weird rattling sound when cold. With that being said I’m starting to look at options before something fails on me. I would love some input on the following:

-Possible L33 longblock swap (about 100lbs lighter than the iron block LMG and a little more power), wanting to know if everything from the electronics of the LMG will work with it.
-Possible 6L90 swap, might as well upgrade if I’m going to change the trans, but what is required to swap since I believe it is 1 in longer than the 6L80, and would it be worth it?

Thanks in advance!

Click to expand...

"P015b&d"?

Your LMG has the same power or more than the L33. The L33 is a Gen3 block so you'd have some work to do to make it work in your Gen4 platform. If building up from a bare block, it wouldn't be such a big deal. But you said an L33 long block which means you'd have to tear down the rotating assembly. The Gen4 rotating assembly is a little stronger design as well. IMO, that weight savings from the aluminum block is negligible and not worth the hassle involved in retrofitting an L33 block.

I say pull the plugs and scope the insides of the cylinders and run a compression test. If that's all good, then just delete the AFM (including plugging the relief valve port in the oil pan), install the upgraded driver's side valve cover (if yours is a pre-2010 year model) and swap in a performace cam if you want. This would make it feel fresh again and may reduce or eliminate the oil consumption. Get a tune to turn off AFM and tune for the cam if you get one but also to clean up the factory transmission shift tables.

Buuuuut, sluggish performance, rattling when cold, some sort of P015x code... What all have you done to address this code? If I'm not mistaken, that's an O2 sensor code of some variety. Could it be that you have a failed cat converter that has a broken catalyst that rattles until it expands and "braces" itself, but also is slightly clogging the exhaust? This would induce the symptoms you've listed so far.

You may just need new cats and a full maintenance job performed. Spark plugs, induction cleaning (including the MAF- which could cause sloppy or harsh trans characteristics), all fresh fluids, a thorough scan with a good scan tool and maybe reset the fuel trims, etc.

Welcome to the forum from Oregon and wait for all the recommendations coming your way. Pics of your rig please.


We recommend that you put all your rig(s) info in your signature so we all don’t have to guess at year, make, model, engine size, trans, rear axle locker…….etc. While you may have posted pertinent info in your first post, you may forget to do it again and the info is needed by us anyway. Makes it way easier on all members that attempt to help, to have that info right up front. It is also recommended that you take a pic of your RPO codes, on the inside cover of the glove box, and post that image in your signature. All this info will greatly help those that will try to help with a problem.


If there is any other info, like upgrades, mods or recent mechanical/maintenance work done, that would be helpful in any post as well. Too many times a question is asked by the poster and after about 10 responses we find out that the poster has done recent work to attempt to fix the problem or work that was done that SEEMS not related to the problem.