That Flowmaster muffler actually restricts flow more than the OEM muffler does, that may be part of the problem with your low end feel. Your truck is actually restricted more than stock wit hthat on there. What is the diameter of the pipes they used on your truck. Should be no larger than 2.5" for a dual set up and 3" for a single exit.

Is your truck is not tuned for "premium" fuel that may be a problem? Did the truck shake like that before the exhaust install? It is possible that the K&N filter was overoiled causing your MAF to act up and may be causing the shake you feel, but it should be more like a sputter. I would suggest getting the problem fixed before making any attempt to tune the truck because thing may get worse once a tune is installed.

If I were you, I would get some MAF cleaner and clean that, then install the OEM filter and see what happens. Also try regular fuel since yo uare not tuned for premium.

 

I have tried putting the stock air filter back in and cleaned the map sensor before I put it all back together. I can try on the next tank not to run premium. Would I be ok to just run regular gas instead of ethanol? I can put the oem filter back in again and see what happens. Beings it already has a different exhaust system on it that is welded in should I have another muffler installed? If so what do you recommend? I am already $600 into this with the exhaust so I really do not want to start over. They still have the factory muffler I could have them put it back in and just put a y pipe after the outlet for the dual tail pipes. The dual tail pipes are custom that the muffler shop made would that cause the problem? They are 2.5 inch outlets on the muffler. The tailpipes were bent with a ram style bender. If I remember right the truck did shake a little before the exhaust while climbing hills.

 

You won't have any issue running 87 Octane fuel, that's what your truck is designed to run. To run Premium fuel, yo uwill need a tune that will be able to advance the timing to properly burn the higher octane fuel.
You mentioned MAP but did you clean the MAF sensor? Also make sure it's installed in the right direction if you had taken it out before. You pipes the shop made seem to be the correct size for your engine so that's not an issue.
Did you oil the filter when you got it or just install it out of the box? Should have been oiled at K&N so it does not need to be oiled before being installed by the customer.

Keep the exhaust if you like it, no need to be throwing away that kind of money.

 

Yes I did mean the MAF sensor sorry. I have not cleaned the K&N since I bought it. So therefore I did not add any oil. It was a cooler day yesterday highs only in the 70's and the truck seemed to run better since I put the stock filter in and cleaned the maf sensor. Today it is supposed to be warmer so we will see if it acts up again. When I have noticed it acting up it has been in the 90's with high humidity. The MAF is installed in the right direction. I ran the tank down to 1/4 yesterday beings I have always heard that if you go below that the fuel pump becomes exposed and can heat up. I filled up this morning with Road Ranger 87 Octance fuel. I read online at http://www.toptiergas.com that road ranger was a good place around here to get fuel. I used to use BP and suprised to see they are not on the list so I will try not using that for awhile. All the local mechanics all swear by BP premium saying it is the best gas out there but maybe not anymore. I will post my findings after I drive it today.

 

Your not going to hurt your truck or cause any issues by running premium fuel, but it is a good practice to change gas stations if you notice any performance issues, just in case it is poor fuel. Let us know what you find. I have had exhausts and CAI on all my new trucks and have never suffered any performance issues.

 

The Top Tier gas list is a joke anyway..You have to pay a price to be put on that list.

Shell is on there and it's the worst possible fuel you can run. More detergent than gasoline in that stuff. Known to cause a lot of problems with tuning.