Same thing happend to me i had cai exhaust and diablosport. then went with a servo 4.10's w4me tune and went .2 slower

 

I'm sure the 20's aren't helping your cause much either....

 

I ran that same 1/8th time with my 4.8 with mods in sig minus the 4.10s, truetrac, pulley, I had 3.42 and an open diff when I ran that time. My 60ft was the same as yours but my MPH was like 3-4MPH faster... I know my 60ft suck because of low timing in the low RPM/high load areas... I have since adjusted it some it is better now, but I have not gone back to the track.. So I think it is in your tune as well...

 

i think you all are right about the tune, when i go to do a burnout, it will stop spinning once the truck moves forward and shift into 2nd then downshifts back to 1st. and it only tops out at alittle over 110 at 5500 with a 29" tire. it should be faster then that right