I have a 99 K2500 Suburban...180K miles, (mine is a 5.7 however). You failed to mention any Check Engine codes???
GM Vortec 101: If you have no codes, its probably a "hard" part. These motors are sometimes difficult to troubleshoot because many of the hard parts will go on the fritz and not trigger a code. Most noteworthy is the ignition system. This sounds like a classic cap/rotor/wire problem to me, and I've had the same issue several times. My truck seems to eat caps & rotors, and I rarely get 50K miles out of one. It also only seems to like the $80 AC Delco cap/rotor set. I've tried other brands...but, nothing works as well as the Delco parts.
CAP & ROTOR The rotor tends to fail first, and upon inspection...you can see a small brown spot under the metal contact (in the center of the rotor). This is where the electrical arc is actually jumping thru the plastic rotor and grounding-out on the advance mechanism underneath it. Obviously, you need that current to flow thru the wire to the plug but, it always follows the path of least resistance...so make sure you got fresh plugs & wires, too. You'll probably see some green cheese on the terminals inside the cap...this is caused by moisture, and I've noticed a huge improvement using silicone spray....so ALWAYS USE SILICONE SPRAY WHEN YOU INSTALL THE CAP & PLUG BOOTS. It seems makes a giant difference on Vortec motors in particular, because of the temperamental ignition system.
DISTRIBUTOR GEAR While you're at it...you will want to check the gear on the end of the distributor. These are engineered to wear faster than the cam gear and I've seen many of them totally fail at 150K miles. Be very careful to mark your rotor location if decide to pull the distributor....otherwise you'll be hating life trying to get it re-indexed properly. Look for sharp teeth on the gear...if they are worn and "pointy", its junk. Don't bother replacing just the gear because the stock distributor is a total piece of plastic crap and not worth saving. Instead replace the entire distributor with a new billet aluminum version. These run under $100 on eBay and come with a new gear already installed. Made in China...these are a drastic improvement over the stock plastic OEM version. They usually come with a Chinese cap & rotor but...as I mentioned above, you should upgrade to the Delco versions.
SEQUENTIAL PORT FI SPYDER This is another simple way to drastically improve a Vortech. In fact, GM dealers do this conversion when they replace fuel injectors. It basically replaces the troublesome 2-injector stock rig, with a new 8-injector rig. These conversion kits run $300 and take a couple hours to install, (do this work along with intake gaskets).
INTAKE GASKETS Look at your intake and see if you notice puddles of green anti-freeze sitting on top of it. Vortecs (all of em) are famous for leaking intake gaskets, and they can also leak air (vacuum). I can tell you without question...if you haven't replaced your intake gaskets at 150K miles...you need to. A vacuum leak can play hell with your drivability, and it could certainly be causing the cold-weather hesitations you describe. You don't need a propane cylinder to check it...instead use an incense stick (hippy-stick). These will put out a steady stream of smoke, and you can run it along the base of the intake and clearly see if the smoke gets sucked-in anywhere. I usually like to put on some Doors - Morrison Hotel, when performing this check.
BTW...this same info applies to all Vortec motors. They are remarkably similar in terms of fixes & upgrades regardless if its a 4.3v6, 5.0v8, 5.7v8, or a 7.4v8. They all share the same basic parts, and have the same basic issues. These are the last generation of REAL chevy motors, before they went distributor-less and reconfigured everything. They are also the last real DIY motors, and you can work on them yourself without a scan tool or special equipment. They are finicky but, once you get them figured out...they're easy to maintain, make good power, get good mileage, & they're very dependable.
