99 vortec 5.7 tune with t56 can't fix limp mode

[RSTahoe99]

So i have swapped my auto for a t56. I turned off all the transmission dtc's and changed the tune to show manual transmission. I corrected the speedo and flashed the computer on the truck. For some reason the truck keeps going into limp mode with/in seconds of cranking it up.

What am i doing wrong? I have attached my tune if someone could take a look at it.

I appreciate any and all help.RS_1999_Tahoe_t56_0400_transdtcsoff_2_0000.tun

[Aloicious]

I took a quick look and I couldn't see anything problematic with it. even compared it to a '98 stock manual tune and couldn't see a any potential issues. are you getting any codes or anything?

[RSTahoe99]

no codes. I am assuming no codes because i turned off the dtc's for the auto trans.

[Aloicious]

well yeah, I meant different codes that might cause the same issue. I don't know what to tell you on it. you should get it swapped to a 411, we've already got the auto to manual bugs taken care of with that.

[RSTahoe99]

i will wind up doing that. I just wanted to figure this out and finally get it on the road. I still haven't put 100 miles on it since the t56 swap

[Aloicious]

yeah, its got to be something else, either internal to the PCM that we can't access, or another problem causing the issue, because I can't see anything that would cause it in your tune.

[RSTahoe99]

thanks for looking, i've been banging my head against my laptop trying to figure out why it won't work. maybe someone that has run across something like this will comment, but in the end i know for sure the 0411 swap will fix it.
It just bugs the crap out of me knowing there are manual trucks outhere running the black box and i can't figure out how to make it work

[Aloicious]

yeah, I'm halfway wondering if with the blackbox PCM, something is hardwired for auto vs manual, kinda like the 5800 rpm limit that is internal, or perhaps its OS related, since all I can find on your OS in the tune is that it was used in automatic L31 1999 suburbans...I can't find any stock tunes for a 1999 GMT400 L31....there are '98 ones...you could try flashing in a '98 manual trans OS and see if that helps...

I'm just kinda thinking outloud here though, I can't think of anything else that would cause that problem