Towing capacity for 92 1500

I Just bought a 92 1500 GMC Sierra with a 350 auto, low miles. What would be the towing capacity of the truck? I probably won't tow anymore that a 3000 lb boat. It is a 4 speed auto transmission. If tow very much would you recomend a shift kit or transmission cooler for towing light loads such as 3000 lb? Should you tow in 3rd or 4th on long trips? I'm new to the Chevy/GMC line of trucks so any info would be helpful.
Also any advice one good brakes or upgrades would be helpful. Thanks, Lance

not too sure on the 92, but heres what my manual says for the 97 with an auto and 350:
2wd Axle Ratio Max trailer
3.08 5000 lbs
3.42 6000
3.73 7000
4wd
3.42 5500
3.73 6500

So really whichever combo you have a 3000 lbs boat should be no probem at all. Personally I tow in 3rd in the city and 4th on the highway, although my manual states I can use 4th under all circumstances. I would however invest in a tranny cooler if you're towing frequently, hell they're less than $100 , to me it just seems like cheap insurance. As for brakes I've towed somewhere around 4000 lbs with the stock brakes, but I would defiinitly recommend trailer brakes for a boat, they may even be required by law where you live, again a brake controller runs at less than $200 installed, best bet is to visit a local trailer shop for that one though.

Thanks for the information.