had my truck 3 years now and have 65000 kms on it. for the first 6 months all seemed well. but since that the power just isnt there, 3000+ rpm to hold speed on the slightest hill. last weekend i towed my atv out over the hiway , probably 1200 lbs counting the trailer, and could barely manage 11 mpg, 4500 rpm on hills to maintain speed and very slowly pickup. iv tried a few things but no sucess, at one point had a cold air intake, mbrp exhaust and a diablosport programmer but could feel no noticeable difference over a couple months so i sold the intake and programmer but kept the exhaust cause i like the sound.is anyone elses 4.8 like this? dealership has hooked up it many times and say everything is right.near 300hp shouldn't struggle like this. any help or suggestions? truck is a 2010 silverado 4.8 with 3.42 gears , mbrp exhaust and 285/70/17's on a 2" level. tires and level have been on since day one and any helpwould be great.