89 Dakota 3.9 2WD. I've had an odor of gas from the area of the fill tube and rear wheel opening for some time, but no actual leak. I put the trucks rear wheels on ramps to work on the shocks. When I started the engine to drive off, I had a heavy leak of gas cascading down the tank. Shut the engine off and it stopped. Just trying to narrow down what the issue is.

Only when running tells me either the senders rusted out or a line. You need to look harder, maybe with a mirror.

Sender??

Fuel tank sending unit. Might consider getting it to a shop before you blow yourself up.

Isn't that all one unit with the fuel pump? Nah, no explosions!

Might be. If so you are pretty much out of luck.

sure sounds like the sender, or around the area where the main line connects to it.
could also be the return line, but i'm betting when you get the tank down, it will be super easy to see exactly what the problem is.
as an aside, it "may" be easier to remove the bed to get to the top of the tank.
just depends on how rusty the fasteners are, or the ease in which to get to them.

I was thinking the same thing!

On an 89 Dakota, I'm betting it is the fuel line just out of the sender/pump housing and goes to the fuel filter on the driver side inside frame rail, especially if the line is still OEM. I don't want to count how many of those lines I have replaced over the years. The steel lines like to rust through at the bend where the line curves around the tank, before it reaches the frame. They are not fun to fix in that location, I would plan on changing the line at least up to the filter, but probably all of both lines. It is easier if the bed is pulled, 8 bed bolts, pull the rear bumper, wiring to the tail lights, and the fuel filler off the bed side and lift straight up.

If that is where the fuel leak is, I would also take a good look at the rest of the fuel lines on the truck. Replace them all at the same time. If you have not replaced the rear brake line that runs along the frame between the tank and the frame, i would do that as well at this point.

absolutely !
anytime you find rusty brake lines, the fuel lines are rusty as well.
and if you are doing some, do the whole system.
that is only going to be a couple of bucks and a couple of hours more to do the who shootin' match.