surge/miss at cruise speed when engine is under load

[pawngod]

my 08 sierra denali w/u1794 87tune , 91octane... i have been getting a surge on the sd at cruise speed around 55 when i am going uphill or slowly trying to increase speed. it feels like a plug missing..i finally realized after weeks of this..the surge or missing feeling is the transmission .......i had used the cruise control and noticed i wasnt getting the surge ...the difference is..under crusie control and going up those hills,, the trans drops down to the lower gear....when i am controlling it by foot...and giving it the slightest more gas to maintain speed...it seems to be trying to decide what gear it needs to be in...over and over several times or as long as i am giving more gas to maintain speed............when i give it the tiniest bit more pedal it will downshift.....the spot between actually downshifting and not...is where i am getting the plug missing feeling ..the hickup or surge ...anyone else experienced this?

[mikel]

Hmmm....are you really, really sure it is the tranny, or could it be going in and out of DoD...?

[pawngod]

not absolutely positive its the trans....but really strange...even the slightest more gas pedal..and it downshifts ..i currently have the dod off..i have had trouble w/speed limter till i added 9r05 crom......was not able to tell before new crom if dod was off or not.....i was not able to feel the difference when it was on...so not sure how to tell difference when its off...after new crom and i turned it off..it seemed to downshift quicker w/o lag.....it dont have the surge when cruise control is set...it just downshifts under load going uphill but i wish it wouldnt..i would rather be able to give it a tiny bit more gas w/o the downshift

[CANUCKPREDATOR]

do you have driver information center? if you go to instant fuel mileage it will say v4 or v8

if not watch you tach very close, when it goes into v4 it will jump about 50 rpm (a needle width) and drop same amount when going to v8

[pawngod]

i have it....i got it to do instant mileage..but never saw the v4 or v8 part of it..on my tune i was unable to get the star removed from the dod when trying to turn it to ON... to see if it still has the on-off on-off on-off feeling.

[CANUCKPREDATOR]

unless the 08s don't have that

guess you'll have to watch you tach.

[pawngod]

its jumping alright..lol.....i got the dod turned on and star removed..i reset all and started over w/my other ltft and speed removed..test drive it a couple weeks and just check my fuel mileage w/it dod on and see it surge disappears now

[CANUCKPREDATOR]

i've heard the 6.2l have had that issue of surging with DOD. This is GM issue, not a tune issue. Might want to talk to dealer about it.

[pawngod]

WELL... i am an idiot...i just found out after owning my 08 sierra denali truck for 2 months..it aint go no DOD or vvt or anything..was not offered on the 6.2l....so i dont know why but,, when i changed the dod to off on the ds is most certainly has more response on quick downshifts....i removed the asterisk form the tune and its back to the old slow downshifts through each gear...w/ the dod was turned off... on the ds....it drop form 6th at low speed cruise straight to 2nd or 3rd (depending on the speed) thats wierd...that it can effect the shift performance even though i have no dod? anyway...i seem to be getting better gas mileage w/the asterisk removed on dod ds tune and i havent noticed the studder surge or foul plug feeling w/dod off

[mikel]

Interesting....