The tow rating for a manual transmission is less than an automatic. I think the reason has to do with clutch slippage needed to get the mass moving from a dead stop. 4,000 lbs up a steep boat ramp might hurt the clutch.
Can you tow 4,000 lbs with a manual transmission? Depends on terrain, altitude, temperature, vehicle condition, load in the truck, distance traveled and ability and experience of the driver.
Regardless, I would not tow 4,000 lbs without trailer brakes.
Isn't the H3 much heavier than a Colorado? Right there you have an advantage over a H3 with the same drive train.

 

I am new on here and I have some towing questions too.. Had a great experience with my 04 z85 so far approaching the 100,000 mile mark now and just got a 3500lbs travel trailer pulled it home about 50 miles felt fine i have been told a tranny cooler would be a need especially when i fill the tanks.. just wondering if anyone is towing alot with this truck and does anyone have good solid advice.. ::chevy::

 

a cooler is not a 'need' but its good to have. i tow around 5-5500 with my 05 Z71, auto. shes pulls it....not too happy about it, but she does it. coming soon is a cat back and CAI. i added airbags, which help alot to level it out, front truck pads and a trailer brake. i feel with a tune and bolt ons, itll be better all around. by next year i hope to have a trans cooler also.

3500 is no problem. theyre rated at 4000, at least mine is.

 

I don't know about the stick shift, I have the auto, but 4000lbs is a LOT for this size truck. I just got back from a 3500lb drive out to Arizona from Ohio (2000 miles) and a 1800lb drive back... It will pull these weights, but I got 11+ MPG loaded and almost 15MPG empty on the way back. After fighting the transmission wanting to run in 3rd all the time, I'am going to be looking for a bigger truck after the first of the year! If you are going to haul that kind of weight and only go short distance, and not too often, I'd say it's OK.... But if you want something to do long distance... forget the Coorado, be it auto or stick... it's just not got the balls to do it!

 

Here's a similar thread I started last month. There's some impressive pulls in here.

viewtopic.php?f=1&t=76351&hilit=towing

Good luck.