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2004 chevy trailblazer_ls_ext
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I bought this Sept 2017 with 134,000 miles on it. Body is in pristine condition and has all the service records from day one. Within the first 1,000 miles I was getting a MIL light and code P0128, so I switched out the thermostat. That seemed to solve that problem. This spring when the weather started warming up I was driving home on interstate at around 75mph, bucking a pretty stiff wind, and all of a sudden the rpm's shot up to 4500 and I started losing speed down to about 55mph. I would let off gas and I could slowly climb back up to around 65-70mph and the same thing would happen. At one point the MIL light started flashing. It seems to be sputtering or missing. The only code I can pull from it is P0172. After reading many threads and watching countless You Tube videos I'm completely stumped. The things I have replaced or checked are as follows:
-Replaced fuel filter and pressure checks out at 55psi key on, 61psi at 2500 rpm(Harbor Freight tester, but pressures are consistent)
-Fuel regulator holds vacuum and no fuel present in hose
-OLF,air filter
-Replaced plugs with OEM iridiums
-Replaced intake and throttle body gaskets
-Cleaned throttle body
-replaced Cam Position Sensor
-Seems to be no vacuum leaks(I don't have access to smoke machine)
-I borrowed a Snapon Ethos scan tool from my brother for the weekend so I will be playing with that.
-So far shows no misfires and all injectors triggering.
-O2 sensors seem to be fluctuating as they should
-MAP sensor reads 28-34 and spikes to 50plus when I rev the engine
I know this is alot of babbling guys, but I need some advice on what to look for next. I can't keep throwing parts at this hoping it's going to fix it. My brother is thinking it's transmission related. I'm not quite sure what I should monitor on the transmission to make sure that's working properly. I just don't understand why I'm getting the P0172 code when it acts up. Any advice is greatly appreciated.
 
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