I've got a 07 Avalanche 5.3L flex fuel with Vin 3 170,xxx miles. For a while the truck has had an issue with starting, it will start but sounds like its going to die for the first 30 seconds to a minute. After several months a code finally sets and its the p0449 Evap solenoid circuit. I put the scan tool on it and the first thing that drew my attention was the fuel trims on both short term and long term fuel trims.
OL and CL
SHRTFL1 -3,1
SHRTFL2 -3.1
LONGFT1 -30.5
LONGFT2 -30.5

Change the Evap solenoid thinking it would some how fix these issues......you guessed it nope! Code P0449 goes off and we get 2 new codes p0172 p0175 Bank 1 and 2 running to rich after he drove it.. So grab the scan tool and see the fuel trims
OL
SHRTFL1 -21.9
SHRTFL2 -21.9
LONGFT1 -5.5
LONGFT2 -5.5

In open loop I did see if there was any change at 1000 rpm, 2000, and 3000. The only time the SHRTFL1&2 changed was when I hit 3000 and let off the gas they went to 0 on both banks then shot back up to 21.9.
CL
SHRTFL1 -2.3
SHRTFL1 -2.3
LONGFT1 -30.5
LONGFT2 -30.5

In closed loop 1000 rpm no change, 2000 rpm SHRTFL 1&2 shoot up to -15, 3000 rpm they go up to -26 let off gas and SHRTFL goes to 0 and goes right back to -2.3.

I've checked everything I can think of, MAF, MAP, Air Filter, Spark plugs and wires. No hose is cracked or torn.
The only thing I did notice while running live data on scan tool was the Alcohol % was 74.9. Yes it is a Flex Fuel but we have never in 3 years put E85 in it and our gas stations should only be 10% or less. Spoke with a mechanic here and he told me that couldn't be the issue, has to be vacuum leak but I do not think it is. Any help would be greatly appreciated. Thanks!!!