New Cat and cat-back, surging/bucking

Last weekend I threw on Rustys TB spacer and 6x9 K&N with the air tube. Ran beautifully. I took off wednesday this week and had my local muffler place throw on the $131.00 cat from AutoZone and Rusty's mandrel bent 2.5 pipe with the Flowmaster 50. Ran great. Until 5 miles on the highway. Started surging and cutting out just cruising on the highway. Check engine light popped on at the sametime. Didn't matter what speed, if it was underload, uphill, would completely cut out...then all the sudden "catch" and flow the whole vehicle. At its worsts, it would buck the whole heep back and forth, almost as it if was bouncing off the rev limiter and back. I was searching all last night and came up with a few things.
1. I know the fuel sending unit was replaced in 2000 by calling the dealership. However, I have to do the crank key to run, 3 times to get it to start without cranking 3-5 times. Plus it fires right up.
2. Muffler shop man "said" the O2 sensor was okay....??
3. CPS and CKS....I can't really try to check them now as I got to to my mechanics to save a tow (don't have towing with my auto ins)
4. I heard something about "Flashing" the computer after a new Cat is put in?? And it has to be done at the dealer?
I'm trying to think if I forgot anything. It runs like a new jeep til about 4-5 miles down the road....then lookout. I knew I should have done plugs n wires when I did the intake, but I'm not thinking it would fire up and idle fine cold if it was plugs or wires. When warm it idles rough, spiking up and then almost stalling.
97' Sport, 102,500 miles, 4.0, Auto. Really would like to know about #4 above. Because that would suck to drive it to the stealership. FSM supports this somewhere Im pretty sure.
Also, Bosch O2 sensor okay if thats what it is? I have one.

As always, thanks....check back in at lunch.

sounds like 02 sensor. When my 02 sensers went bad it would do the same thing, just buck/surge horribly. It would die out and then jump back to life, backfiring in the manifold horribly every few seconds. Replaced the o2 sensors and runs like a top.

BTW, mine is a 98. Yours has OBDII I believe since it's a 97. They are very picky with 02 sensors. did you get a CEL?

Never heard of flashing the computer when you change the convertor. If you don't KNOW the condition of your spark plugs, check them. When the gap gets too big from old age, one of the signs is missing under acceleration (like it won't "take" the gas).

My '91 would surge and buck when my stock header was cracked at the collector. Try looking for an exhaust leak.(Since you just had exhaust work done). I think it has some thing to do with little back pressure in the system. I dunno Just trying to help.