06 toyota tundra gas mileage

So I just got a whole new exhaust with catalytic converter and my gas mileage went down the tubes .I now get 12 to 13 and yesterday pulling a enclosed cargo trailer with about 1200 lbs I got 7.5 mpg.Before I was getting 15 to 16 mpg not pulling a trailer. Why did I lose 2 to 4 mpg when mechanic thought I would get a small increase?

 

It may help to reset the mapping by disconnecting battery cable.

 

Thanks will give that a try and get back with you.

 

Pulling a trailer will significantly reduce your mileage epecially with stop and go type driving or strong headwinds.

 

When we pulled my truck back from Dallas with my buddy's 08, we were seeing 9 mph avg. 7.5 seems low.

 

Winter blend gas, cold weather, tire pressure, wind direction, etc... too many factors to list that can effect gas mileage.

 

Thanks 8mint8 that did help now getting about 16 not pulling anything