Bought a Broken Down 2002 reg cab Short Bed 4.8 CAN USE HELP! WONT START

[ChevyTruckGuy]

Here is info about this truck http://67-72chevytrucks.com/vboard/s...d.php?t=618250
Now 6 months later......
I bought my friends 2002 silverado after it broke down at the job site. Hes original owner, I have been around this truck its entire life. He gave up on fixing it & accepted my $1000 offer. Its has no major dents, some scratches, interior okay. Rust free, not a bed truck, id like to keep it & make it a regular driver, I bought it & registered it last week. Had it towed home.

Now the truck has 340,000 freeway miles, no big deal for me. Its a 4.8 v8.

It ran perfect until he got to its last destination. It cranks but doesn't start. He replaced the crank censor, added new plugs & wires & replaced another censor but I dont remember which one. Well I got it new & when I spray starting fluid in the throttle body it fires for a few seconds, so I think its getting spark. I went ahead & replaced the fuel pump thinking that was the problem, 4 hours & 300 dollars later it is the same problem. Still no start. I replaced fuel filter & fuel pressure regulator & still no start, another 75 bucks. Funny think is the fuel gauge on the dash reads an empty fuel tank when its 3/4 full. Dash is also saying low fuel. I hooked up a code reader to the truck & its sending out a error message. Now doing a google search im finding folks are having a problem with the theft part of the truck, as if the truck thinks its been stolen. Also im thinking its the computer it self maybe. The pump thats in the tank is very quiet unlike my other chevy trucks. My brother is helping me fix the rig & WERE STUMPED. The relays seem okay because the truck has a few of the same & I swaped them around a bit & still nothing. I added a new battery just in case but didnt work... Maybe a bad ground? Can we wire the fuel pump direct to the battery & not damage it? My friend said he hooked up a pressure gauge to the fuel rail & it read it has enough lbs but I didnt confirm this for my self, just assumed it was the pump like my other trucks. I cant confirm it has spark, I put spark plug in wire & grounded it out & didnt notice any spark

Thats it for now, I can only work on it when time allows, once a month, THANKS for any advice & ill get pics soon.....