pump running little water going into tank
There could be several reasons for this to occur.  The first thing I would do is install a new pressure gauge.  From your description, even though the pump is running it does not sound like it is "primed".  If pressure is built in the pump when you pull the "prime plug" the water would be shooting out of there.  The best way to prime a jet pump is to install a ball valve where the prime plug is so you can add water here to the pump as it is running to help "prime the pump", regulate the amount of water going in, and begin to build pressure.  As the pressure on the gauge begins to rise shut off the ball valve and see if the pump begins to build pressure itself. If not continue to add water as pump is running until the gauge shows pressure building.  It would also help to do, as you did, (shut off the valve between pump and tank) until the pump builds pressure in the line. Then gradually open the valve to the pressure tank, watching the pressure gauge and trying to keep the water pressure on the higher end until the tank is full and pump shuts off.  If the pressure tank is waterlogged (No Air) the pump will have a considerably harder time to build pressure.


Jet pumps generally have a 20/40 pressure switch. Any higher pressure can cause the jet pump to work too hard to build and maintain pressure.  
If there is a galvanized well tank make sure it is pressurized to 18lbs of air with a 20/40 switch. 28lbs with a 30/50 switch. This style tank has to be re-pressurized yearly.
If it has a bladder style tank make sure the air charge is the same as above.  
You also need to determine if your well pump system is a single drop or double drop design. [Double Drop and Single Drop Jet Pump Well Designs][1]
Get yourself several buckets of water to aid in priming the pump.
If none of this helps you most likely have a plugged screen (call well man) or bad check valve (The check valve may be right at the pump). You can replace that yourself. The sign this is bad is after the pump builds pressure it immediately kicks on again as the check valve is allowing water to drop back down the pipe causing the pump to loose prime again.
Jet Pump Trouble shooting
How to re-pressurize a well tank 


I hope this helps, 

R.J. DeChene
The Water Softener Blog.com