Steering Problems

I have a 1994 Dodge Ram 250 Van 3.9L V6 automatic with 83,000 actual miles. About six weeks or so ago i began having steering problems with this Van. Whenever i tried to make a turn it seems as though I lost my power steering and was steering in manual steering. I just started out of the blue and lasted a few days and then went back to normal. Then it started again. I figured the power steering pump was simply going out for I had no leaks and the front end was aligned and just fine. I installed a new (autozone) power steering pump, new power steering pulley, new pressure line and new return line. I bleed the air out of the pump and lines by running the engine and steering left and right for about 4o minutes. I then test drove the van and again it felt like I was manual steering when trying to turn. Regardless of wether I was just idling or racing the engine up. I figured it was just some trapped air in the pump or lines. I went ahead and greased the front end and all the tie rods which everything was in good shape. I drove the van around for a few days and then it worked perfectly. Steering was perfect. This lasted for about a month and now the steering is back to the way it was before I replaced the power steering pump. When I try to make a turn it is as if I have no power steering. Its like manual steering. I dont understand it. There are no leaks, the fluid level is fine in the pump. When I drive down the highway there is no shimmy or shaking nor does it vibrate or pull left or right and the tie rods and front end seem just find, so I have ruled out any problems with the tie rods or suspension. Surely the new power steering pump cannot have gone bad in this short amount of time. I just don understand what the problem could be. My Dodge dealer said they would replace the power steering pump and the power steering gear box to eliminated all possible problems. another words drain the pocketbook for $3,000 as they quoted for the repairs. Money I just dont have and cannot possibly get, for i live on a fixed income. I have done alot of mechanic repairs on my vehicles over the years but this situation has got me stumped. I dont know if the problem is in the power steering gearbox mounted on the frame or what it could be. I have never messed with a power steering gearbox before. Any help or suggestions anyone could give would be greatly appreciated. Thank You very Much and God Bless.

Sincerely Ann