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2003 gmc

When driving on the freeway at 75 mph the tach reads 2400 rpm’s. The mpg are running 13.5. This doesn’t seem right. Help. The truck is an automatic with a tow package. It is 6.0 liter with a V-8 engine.

Are you saying that you’ve had better gas mileage? I don’t see too much wrong with what you’re reporting. It’s when I see someone like yourself reporting 18mpg that I start going (cough-cough). You’ve got a 5700lb brick into the wind @ 75mph.

What do you think is not right? RPM too high or low? MPG too high or low?

I will add that those mileage read outs are not generally all that accurate, but they may be very good on some cars, but with another driver they can be off. If you really want to know the real MPG you need to measure the miles and the gallons and do the math.

I assume the truck doesn’t feel right, that it seems that used to be much more free-wheeling at this speed and now feels as if it is revving too high. If so, your tow package may be at fault. You would want more torque while towing and you would hopefully drive at lower speeds. See if there is not a manual method to engage the towing function and make sure it is off.
If it is off, then be aware the MPG for a GMC 2003 V-8 varies according to vehicle, with a low around 12 MPG to a high around 21 MPG. At 75 MPH, you cannot expect to get the optimal MPG for your vehicle: it would probably be as low as the city mileage. If this is your complaint, leave earlier and drive slower.
Find your engine and model and see what the MPG should be.

My “98” Chevy 3-door pickup with a 5.0 only manages about 16 highway miles and that’s at 60-65 mph. If I drive it any faster my mileage drops considerably. It also has a tow package and runs about 2500 rpm at 75mph. I think your readings are right on the money.

What do you think it should be and why?

I guess I didn’t explain myself well. I recently took a 3000 mile trip. (Arkansas to Washington state) My concern is not for the milage (although 16 would have been my guess) it is the rpm’s. The truck feels like it needs to shift. I have a 2003 Mach truck that at 1450 rpm’s will do 60 mph. I would have thought that at 1600 rpm I should be at 70 mph at least in this 4 wheel vehicle. I was not towing anything. I think that my problem lies somewhere between the tranny and the torch converter clutch. It should engage in fourth gear when the overdrive switch is turned off. After all the TCC is suppose to provide a direct improvement for efficiency and economy.

You are right. It doesn’t feel right. The reason for the higher speed was a 3000 mile trip. I was not towing anything. The little tell tell button says the towing function is off. But it doesn’t feel like it is. The MPG was not my concern except to find the problem perhaps. Was looking for a starting point for repair and you confirmed what I thought that it has to do with the towing package. Thanks for the reply. Kim