How much transmission fluid does a 2003 H2 Hummer hold?

well is that hummer that a 2 ton or 4 ton vehicle ?

would take a lot of revs for first gear to make it roll from a standing start
think it will be fitted with an 6 speed automatic transmission

guessing only from my heavy vehicle driving experiences
first should change below 3000 rpm

if transmission was slipping in first gear you would know

suggestion
ring up the local hummer service division for the correct answer

If it's a automatic,the fluid goes in the transmission dipstick.Check while running and in park.

you may need to put a few quarts (2) of trans fluid in it, start it up and see where the leak is from. when its fixed, use DEXRON VI

well now you know the brake fluid have to be change every 20000 or 30000 miles

Yea, hummers are notoriously unreliable. They are gas gusslers too.
I'm assuming this is an automatic?
When the transmissions computer detects any malfunctions, it will give you a check engine light, or something along those lines.
Do the normal checks such as checking the transmission fluid level as per the user manual.

For further diagnostics you'll need to take it to a mechanic. It's impossible to diagnose a problem like this without driving the car and being able to reproduce the problem.

Check the linkage that goes from the shift lever down to the transmission. It sounds like somewhere along the line, it has become disconnected or has broken.
if that parts are clean then It sounds like you have a shift control solenoid that has high resistance causing the hard shift you describe. Scan the PCM for trouble codes if none are present you could have a internal transmission problem.

The radiator has an internal trans cooler that must be leaking, the radiator needs to be replaced and the cooling system flushed of all the trans fluid. Usually the radiator hoses and hoses going to the heater core will need to be replaced because the trans fluid will soften the rubber and make them swell. Good luck, Honda Al

Had the same problem. i have to re-place my front wiper motor they are all connected.

Most likely a defect in the trans from the factory