Looking at a 2011 Tahoe with the 5.3 flex fuel (whatever that means) 4x4. The wife has a '04 with 80k but frame has rusted and we love it....a whole other topic on that....anyway looked at this Tahoe with 104k miles. Super clean. She putted around and loved it. I took over and when I hit the gas at 35 mph or so it bogged....just sat there.... and then kind of accelerated. Her '04 is no speed demon but does not have that bog. Is that normal??? Thanks in advance for opinions!!!