After an accident with the truck in the winter, it's rebuilding time. The truck has the 4.9, standard and is running 33's. I know it won't get great mpg (12 currently) but I want some opinions on this.

I'm getting 3.55 gears in the rear end instead of the 3.08, Synthetic motor and rear end oil and E-fans.

And here's the one I need some help on. It has 136k miles on it. Still has original cats and o2 sensor. The y pipe is getting soft also. Would it be worth the money to buy a new y pipe, "high flow" cat and a new o2 sensor? If so what's the right exhaust size, summit has a 2.5" y pipe for $60. I'm hoping it would help performance/effiecency and also sound a bit better.

 

Gears will help quite a bit and for the exhaust pipe, before cats is 3" I think, after cat is 2.25" the new cat and O2 sensor may help, depending on whether or not they're still functioning properly. A single high flow cat will do better than the stock 2 cats(if you have 2)

 

I knew what the stock sizing is but what I was curious as to what is the perfect sizing for back pressure vs flow. I was planning on going with a single cat also.

 

Not sure if it`s perfect or not, but I stuck wit 2.25`` pipe after the 2nd cat dumping right before the rear tire and it gives a decent sound. Still torquey and good gas mileage

 

have you corrected your speedo for the 33's? also is your truck 4x4? only reason i ask is my dads stock 2wd 4.9 5spd can get 21mpg. i know i had to see at least between 15-23mpg somewhere when i drove it yesterday. started out with 3/4 tank, drove 46.6 miles and then put $20 of premium gas(4 gallons) in it and brought it up to 7/8 of a tank. before you go spending all that money on upgrades you may want to try simple things like switching to premium gas. i know even my dad notices the difference between running the ethanol free premium gas instead of the ethanol laced garbage. even if you just gain 1 mpg from running premium it will usually cover the cost difference. now if you are looking to save a bit more money you could get a air miles card if you don't have one and buy all your gas at shell. for every $20 you get 1 air mile and for every 95 air miles you get $10 off gas but lately that have had deals like buy $50 of premium gas on certain weekends and get 50 air mile which is pretty much like saving $5.