Should the oil in the pump be milky you have to surge the trigger on the gun to get pressure then it stays until let off the gun then no pressure and repeat?

You don't give any clue as to make, model etc so I'm going to guess that there is some wear in the pump which is slightly pressuring the oil chamber when you let off the gun. It doesn't do it running because of the release of pressure to the gun. Yes, change the oil for the correct grade.

You need to give more information. Does the motor stall when you squeze the handle? Does the spray surge and the motor run well? Does the spray surge and the motor surge as well? Does water come out of the bottom of the pump? Does nothing come out of the spray gun when the trigger is squezed?
All of these symptoms point to different problems.
What does your machine do?

Sounds like the gun needs lube. Oil it and try again. 2-3 drops of oil in the hole
where the tank screws on then put the tank back on. Fire it and see how it does.
I havent heard of a low pressure kit for the A-5 but I think it is a waste. There is a rule
with pressure and paintball guns. Low pressure=high volume of air used.
Standard pressure=regular volume. I have 2 a-5's with e-grips and flatlines.
I polished the internals by sanding the bore of the tube (use fine sandpapaer) and
this makes the velocity very consistent.
One thing that comes to mind is that the hammer may not be getting caught on the
trigger latch. Makes sure your gun is assembled correctly. here is your manual.
http://www.tippmann.com/pdfs/products/A5/a5manual.pdf

Disconnect hoses.
Look for kink in water hose.
Check incoming water connection for filter washer
Replace filter washer
If you don't have a filter washer, put one in.
Hook up water, and turn on
Water should come out other side of pump.
Turn on machine.
Do you get pressured water out of pump.
If no pressure, then pump is suspect
Hook up washer hose without gun
Does pressure come out of washer hose
Finally, the gun trigger may be bad.

We had to buy guns now and then.
Search for pressure washer guns
Following link shows guns we used:
http://www.ultimatewasher.com/pressure-washer-trigger-guns.htm

Good news, your engine runs
But your pump may be bad

Here's how to test your pump
Check oil as outlined lower down
Disconnect the washer hose and gun
Connect water hose and turn on water and water should pass straight through the pump
Look for clogs in the hose-end where water hose connects to machine

Turn on machine and see if water shoots out pump
If water shoots out of pump, but no water shoots out of gun, then you may have a 'mud-dobber' wasp clog in your washer line or gun

Look for clogs in the end of each water connection.
Now connect washer hose without the gun, tun on the machine, and see if water shoots out of washer hose
Finally, the gun trigger mechanism may be bad
I don't know which gun you have ... but we replaced guns on our machine now-and-then ... google-search power washer guns for a replacement

Check your pump oil
Pump oil is SAE20 or SAE30 non-detergent motor oil
Pump should be no more than 1/2 full of oil
Use plastic hose to drain pump oil
Do not turn machine on its side or turn machine over or engine oil will run into carburetor

A nail gun works on compressed air.
When you hook the air hose to the gun it fills a cylinder with air pressure.
When you pull the trigger. the cylinder pressure is released onto a firing pin that shoots the nail.
The air pressure line is also connected to the trigger and therefore the trigger has to be sealed.

When ever using a nail gun, you add a bit of gun oil in the back of the gun (not 3-in-1motor oil, it has to be non-detergent gun oil)

If you haven't used the gun in a while, it is best to oil up the gun and let the oil run down into the gun.
If you use anything but gun oil, the seals will give out.

Your trigger seal has given out. It is probably an 'O' ring. You can access it by taking it apart. Look for the O ring.
Bostich makes re-build kits for the different guns that you can buy on-line.
Back when I was in construction, there were several nail gun shops that sold and serviced nail guns, and sold nails to the contractors. I don't know if that business model is still active or if you have to send the guns to Bostich service center.

I'm not real clear on what you're saying, but I think it's that the trigger will not shut down the pressure as it should. It stays stuck on. The other info is how long you've had the washer, but my hunch is that maybe you have hard water, and the deposit build up may be getting the trigger stuck. Try spaying some penetrating oil inside the wand to loosen any deposits that may have built up.

if air sound comes out when you press trigger your pressure regulator pin is stuck-oil gun and attach hose repeate until pin frees or remove pin and clean with brake kleaN oil and replace