Lately, I've noticed that the acceleration is sluggish and the gas mileage is bad. about 2 months ago I changed out all the spark plugs and wires, and the pcv filter, I expected to get better
gas mileage and even better acceleration but no. At the same time I put 4 new tires on, they were not the original p235r70 size, they were p260r70 series so they're taller. Any Ideas as to why the performance is laking and what can I do. I have a '97 f150 extended cab with 130,000 miles on it.

Thanks

 

Change air filter, and the fuel filter. The tires slowed it down though, its a big change. What kind of gears do you have?

 

If you didn't recalibrate your spedometer, your mileage readings are off by about 4.7% too low. IE: If your spedometer reads 250 miles, you really went 262 miles now.

Check that too see if you really did drop fuel mileage.

In reality you probably did lose some mpg with the larger size (extra rolling resistance and weight to get moving), but maybe not quite as bad as it seems.

That being said if you are starting with 3:08 gears and went to a bigger tire size, you are going to definitely get hit on MPG.