more torque and xtra horsepower

have 01 chev.silverado,5.3 6"lift,35inch tires.what to do to get more torque and some xtra horsepower to pull trailer better uphills without getting rid of tires  

I had a 04 silverado with a 6 inch lift. I installed a volant cold air intake system and a hypertech power programmer. It seemed to gain some power but not a whole lot. If you want to get into it id say heads and cam swap.  

Biggest thing would be gears.  That setup needs at a minimum 4.11 gears: preferably 4.55's.  That will give you quite a big power jump, and even be easier on your trans and engine while towing.

Other than that? Besides the obvious engine swap to a 6.0L truck engine, a supercharger setup is about your best bet for increasing usable (under 4,000rpms) power.  

The usual suspects of long tube headers, free flowing exhaust, cold air intake, reprogrammed computer (THAT should be first mod), and ending with a 220deg duration @ .050", .590" lift or lower camshaft would pickup nearly the same power all the mods listed above will give you- BUT it will also move the powerband of the engine up a thousand rpms or so.  Should still make more torque than stock from 2000rpms on up.

But if I were you? I'd do the mods in this order:

4.56 gears ($1000+ mod)
Programmer (tons of options, $300-$400. I'd stick with a big name brand)
Cold Air Intake - aka CAI-. (probably $100-$200. Good rule of thumb: if you can see the air filter in the engine bay, it's NOT a real Cold Air Intake)

Long Tube headers and high flow catalytic converter equipped Y pipe. ($500-$2,000. My preferences are Kooks, Stainless Works, or SLP)

Cam. Comp Cams LSR series would be perfect for you- ask me how I know.  With the above mods, you will find your truck making aprx. 70-80 more hp- but most importantly, you will be making tons more torque from 2500rpms on up: the kinda power that puts a grin on your face everytime you think back to how it ran before. A BIG grin. ---- or just throw a supercharger on there and be just as happy, for $3,000+ more though.

Cat back exhaust? only if you gotta have the sound, they don't gain barely any power on a 5.3L since the factory cat back exhaust is pretty free flowing.  
'05 GTO: 3600 stall, Comp Cams, L92 heads, etc. etc.

'06 ZX14: lots a mods

Gears are a must. Heads/cam are definitely not a bad idea, but I'd opt for a positive displacement blower for torque. The Magnacharger is a nice kit.  

I HAVE A SUPERCHARGED 2004 AVALANCHE WITH MAGNACHARGER,4.10 GEARS EATON POSI,MAGNAFLOW CATBACK AND JBA SHORTY HEADERS.TONS OF POWER AND TORQUE,THE MAIN PROBLEM IS 4L60E AND 4L65E TRANS CANT HANDLE THE AMOUNT OF TORQUE EVEN WITH EXPENSIVE UPGRADES LIKE HARDEND INPUT SHAFT KYRO TREATED OUTPUTSHAFT YOU CAN SNAP LIKE A TOOTHPICK IVE BROKEN 5 TRANNYS IN THE LAST 4 YEARS AND ALSO ON MY THIRD CARRIER SO WITH THAT BEING SAID I HIGHLY RECOMEND 4L80E TRANS AND 14 BOLT CARRIER UPGRADE. THIS WHOLE PACKAGE WILL BE EXTREMELY EXPENSIVE SOMEWHERE AROUND 15K BUT,IT WILL BE WORTH IT.LIKE HAVING A CORVETTE IN A TRUCK VERSION. YOU WILL HAVE NO PROBLEM EMBARRASING FORDS AND DODGES.ROUGHLY 425 FTLBS TORQUE AND 460 PONNIES 0 TO 60 SPRINT JUST SHORT 5 SECS AND BLAST THROUGH 1/4 MILE @13 SECS @107 MPH NOT BAD CONSIDERING CLOSE TO 3 TONS.CHEVY POWER GOTTA LOVE IT....IVE JOINED THIS FORUM TO GO A LITTLE FURTHER I WOULD LIKE TO CAM,HEADS AND FORGED PISTONS BUT WOULD LIKE TO MAINTAIN MY COMPRESSION RATIO TO CLOSE TO WHERE IT IS,I ALREADY HAVE TO USE 92 OR 93 OCTANE OR DETONNATION OCCURS(PINGING) ANY IDEAS.. I WANT TO KEEP THE SUPERCHARGER BOLTED ON..THANKS