Doing that will reduce power for the street. Your thinking is "very old school". Any carb is way less efficient than any fuel injected system.

Get the ECM reprogrammed for torque improvements from idle to 4,500 rpm's.
Install a cold air induction system.
Get a good set of "street" headers that work from off idle to 4500 rpms. None of this race craps the kiddies talk about. This is a "street" vehicle, ...not a race truck doing quarter miles.
If you have 2 wheel drive, change the axle ratio up towards 3.73 or 4.10. That action will force you to correct the VSS value in the ECM.
Get rid of the oversized mud bogging tires and go back to the factory diameter "street use / smooth tread tires.

That should give you a good power improvement.

 

I'm using 265-70/16 8"wheel. No 3rd row-tools,etc. 4wd- I'm 53 but would like to race new stuff occasionally. I've a 12' suburban lt-cold air-magna flow-superchip-4wd also. Just wanna come up from 205HP(3"exaust) i figure gives it a little more than 200

 

Having 4 wheel drive just took out a third of your available horsepower / torque because of all the gears/axle shafts/ heavy axle housing the motor has to overcome.

Your 3 inch exhaust is screwing you over for power. It pushed you torque curve way up stairs to another 1 to 2000 rpm's . You forget you have a "very heavy" truck with a lot of friction coming out of the front axle.

You need "torque", ...not "horsepower" to get you down the road quick with a heavy truck. That is what people tend to forget.

I want you to remember this, ........... Horsepower is "How Fast" something can be done, ......Torque is "How Much" can be done.

If you still believe in carbureted systems, your 35 years behind the times. Computers are more precision.

Never believed in aftermarket chips after what I saw could be adjusted in the ECM software. Performance chips are limited in what they can do compared to a good qualified ECM tuner.

I have one of those "highly modified" ECM's in my little 4 popper. Love waving bye bye to all the macho lifted trucks that can't get over 105 mph or start straining over 70 because they are so high up in the air. It's worth the investment if you find the right tuner.

For what you have, you need idle to 4500 rpm torque power. Anything outside the that point is a pure waste of money and a fantasy to make it go down the road like a race truck.

 

Madddjohn63, Rick has good advice.
A fuel injection system is way more efficient than any carb. In the reverse scenario, a lot of guys like/want to change a carb system over to an aftermarket FI system. Suburbans are not extremely fuel efficient vehicles especially in mountain driving. Lived in Colorado 47 years. 10 mpg was best on a carb-ed subby with some mountain driving.
Old school thinking was a bigger carb and intake equals more power. That only creates more problems. The Camshaft is the heart of the engine and any changes to the intake fuel delivery and exhaust has to be looked at from the camshaft specs and head flow characteristics point of view. More fuel delivery requires more scavenging from the exhaust and that is a main function of the cams grind. It has to breath correctly for any changes in intake and exhaust to produce more torque. A possibility for more low end torque is an RV type camshaft/headers along with a proper ECM program like Rick said.

What size engine do you have?

 

Hey, All. Here's some real world experience with a heavy rig like the 'Burban.

I had a stock L05 in a '94 K2500 extended cab long bed. 6100 lbs curb weight, NV4500 trans and 4.10 gears
Lost the engine after replacing a head gasket but didn't change oil soon enough. Lost a rod and cut the camshaft in half. Stupid.

Anyway, replaced it with the exact engine that Silverado described. A Melling MTC-1 computer compatible cam ("RV" cam) in my replacement long block. Added shorty headers and left the stock single 3" with a high flow CAT.

Resultant improvement in torque was the ability to pull an empty 16' horse trailer up a hill in overdrive that prior to the new block I was only able to pull in 3rd while rolling at 55mph.

Only change to air intake I made was to remove the resonator box and replace it with a flexible 4" downspout diverter pipe. The GMT400's already have true cold air intake from the front bulkhead through the fender.

Standing starts were way more fun because of the added torque.