03 Z71 Tahoe

[biggsteve97]

I have an 03 Z71 Tahoe with 194k on the clock. Starting in about February of last year I noticed my fuel mileage starting to drop and a loss in power below 3000 rpm and the exhaust sounded weird at idle. I have been getting 17-17.8 mpg on my daily drive since I bought the Tahoe in 2006. I changed spark plugs first, no change in mileage or power. Changed wires, no change in mileage or power. I took the cold air kit off and put the stock air box back on, no change in mileage but power came back up some but only for a few months. Changed the fuel filter, no difference. Changed both primary oxygen sensors, no change in mileage or power. Checked fuel pressure and it was 54 psi, same as it was when I bought the Tahoe. Thought maybe intake gaskets, found no vacuum leak around intake or throttle body. about 2 weeks ago I put the cold air kit back on and no change in mileage or power below 3000rpm but power did come up above 3000rpm. about a week ago I cleaned the MAF sensor with MAF sensor cleaner that the gm techs said to use. Mileage came up from 12.8 to 13.9 with a slight increase in power below 3000rpm. The weird exhaust sound went away and an intermittent miss with a consistent stumble at idle has replaced the sound. One thing I have noticed over the last few months is when I am crusing at 35-45 mph in overdrive and the torque converter locks in, the engine rpms drop down to around 1100-1300rpm and the enigne sounds like it is majorly bogged out. If i take it out of overdrive and put it in regular drive for all speeds under 50mph, the engine doesnt lug along but my mileage drops down to 8-9 mpg. I am a loss as to where to go from here. I am almost to the point of selling it.