98 jeep grand cherokee laredo bucking and then dieing?

[Cliff]

I bought a 98 jeep grand cherokee laredo V6 from my sister for $600. The radiator had blown and they had let it set for about 2 years. I had it towed to my house and ordered a new radiator. I went ahead at that time and i did the following: plugs, wires, drained gas tank, checked relay, thermostat, flushed cooling system, distributor and button, new battery, serpentine belt. It started up pretty easy and ran well with a good idle. Then a short time after I started using it on a normal basis it started bucking and would die. So I thought maybe there was a problem in the fuel system. So I dropped the fuel tank. Ordered the filter with the fuel regulator built in to replace it changed that, did not change the fuel pump cause it appeared to be working fine and the gas tank was actually pretty clean. I put the tank back on put high octane gas in it like I had done when I was first getting it running again, ran it in the drive way for awhile and still ran fine until I went to drive it. I would get up to about 30mph and it would buck and die, always starts back up just fine, it would also back fire once in awhile but not often. I made many trips to the auto parts store and kept getting different suggestions from them and friends. I changed the coil next and still did the same thing. The most resent thing I did was cut off the catalytic converter and replaced it with a piece of pipe. Still bucking and dieing after about 20min of running or trying to get it up to 30mph. I would appreciate any help. Thanks in advance.