I just bought an 02 crew cab 2500 and it did not have the owners manual in it. What is the fuel tank capacity? I have driven over 300 miles and it is still showing just over 1/2 a tank.

I think long beds are 34 gallons, while short beds are 26.

I have a long bed myself but looks like I have the 26 gallon tank...Everytime I fuel up it only takes about 26 gallons or so.....not sure why it didnt come with the 34 gallon tank....how can I really find out what size tank I have?

If you fill up when you still have around a quarter of a tank & it takes around 26 gallons or so, you have a 34 gallon tank. Another tell tale sign is when you said you drive around 300 miles and the gauge still shows around 1/2 tank. My short bed 26 gallon tank will show less than 1/4 tank after 300 city miles.

I'll have to pay attn more closely next time. If I remember correctly one time I filled up on #2 and checked my fuel through the steering wheel controls and read like 312 miles or something like that...how many miles should it read if it was a true 34 gallon tank when checked?

CoyoteKid is correct. Nominal 26 on short box, 34 on long.

I'll have to pay attn more closely next time. If I remember correctly one time I filled up on #2 and checked my fuel through the steering wheel controls and read like 312 miles or something like that...how many miles should it read if it was a true 34 gallon tank when checked?
Deppends on how many miles to gallon your getting. I've run mine 600 miles straight interstate driving and put 30 gallons in for a fill up. Can do better if I hold at 65 and not use cruise control. Can do worse to.