89 b2600i gas tank stops filling at 3/4 tank???

So since I bought my 89 b2600i every time I fill it up the pump clicks off and stops filling at 3/4 of a tank. Tried filling it more and gas ran out of the filler neck. I blew air through the return lines and made sure the charcoal canister wasn't clogged. Could this be a sending unit issue? Please help me guys!

Likely a sending unit, does it take a few miles before the fuel gauge starts moving?

Does it ever register full, like after driving it, sloshing fuel around, or uphill/downhill? If not and the dash has never been out of it, likely has been this way from the factory.
Gauge probably needs adjusting, simpler fix, worry about the gauge when it gets low, you are running OUT of fuel (:-)), or pull the instrument cluster out and adjust it.

Yep it takes a few miles before it starts moving, and no its never registered full since I bought the truck. Most it ever goes to is 3/4. The Guage does move and start reading soon as the key is on so idk??

It has not let you run out yet?
Live happily with it, the glass is over half full, until it shows it is not. When it allows you to cough and coast to a stop, I do not like that kind of gauge.
Live with it and polish the chrome to have something to do. I know you must be single, the Hunydo list would nver allow you this much free time,

Lol anyone else think it's the sending unit?

Yes, I agree. My B2000 would rarely show full. Typically it stopped at half tank, unless I was on a steep downhill grade with a full tank, then magically it would show nearly full. I never actually fixed it, just understood that half tank meant half+.

Short of needing to be pulled out of tank, and all that that involves so it can be bent to allow more travel, hence were it the problem gauge does not go to full, when full?
No, it is the gauge.