Bad exhaust valves?

[Dlong30]

Okay guys i need an opinion here. Ive been having issues with my exhaust lately (year and a half) and i think the exhaust valves might be to blame but i dont want to tear down the motor if i have to.

Heres what ive got:
1999 two door tahoe z71
ebay CAI
true duals into 2 flopro mufflers with 2.5 piping out to 3.5 tips
hypertech programmer ( i know im getting the BB tune soon)
3 inch body lift and 285/65 toyo open country at on 18 ultra wheels

I thought that i had too much piping and not enough exhaust flow from the motor but when i hold a piece of paper behind the tips it sucks it back up after every stroke of the motor. My dad used to work as a GM mechanic back in the day and said thats perfectly normal but im not sure. He said it might be cause my timing is slightly off but "its just not gonna get much better from that truck". It runs great over about 3000 rpm and i thought i just need my BB tune but Im also getting pretty bad mileage- 12.5 mpg when i drive easy, 10 if i drive normal city and highway.

So, what do yall think is there anything else i should check first? maybe a vacuum leak? am i just bein picky or should it be performing better i mean i cant spin anything even if i put my foot through the floor while turning. Thanks in advance for any input

Dlong

 

[grimm]

Most will get about 12.5-15mpg in these trucks, but 10mpg seems a little low. Are you consuming more oil than usual or running hotter than usual? Any smoke coming out of your exhaust? Any misfire? Those could be signs of a problem in your valvetrain. If not, maybe you just need a tune or need to take another look at your exhaust setup.

My truck is stock and I can easily spin the tires if I wanted to. So you should be able to as well.

 

[Dlong30]

I havent had any consistent misfires... had a couple of plug wires pop off recently but on the oil issue im not burnin oil but i think my pick up might be loose because my oil pressure will sometimes drop to 0 when i brake hard if im even a little low on oil. ive got a buddy (18 years old) who works for his family shop so im gonna try to take it in there when i get time to get their (his dad and grandpas) opinion lol