97 350 Surging

Maybe somebody can help me out here,

Ive got a 1997 Z71 with a 350 Vortec in it. The truck has been running great
for thwe longest time. It just turned 216k a few weeks ago. For about a year or so my check engine light stayed on and I was told by my mechanic that it was the catalytic converters and the light would stay on until I had them replaced but it wont really hurt anything. Well about 3 months ago the enging started to surge/hesitate the minute it got warmed up. Sometimes real bad from a take-off at a light and even cruisin down the road at 40, 50, 60 mph etc. Didint really matter. I took the truck to my mechanic who has allways done a great job for me and had new plugs, wires and fuel filter put on the truck. It raan good for a few days then started the surge thing again.
I called the mechanic and he said it would be a good idea to get the catalytic converters changed, so I popped the oney and had them replaced.
After that, the truck ran fine again for about 3 or 4 days and started the surging again. I took the truck back to the mechanic and the couldnt find anything at that time and told me to bring it back when it was doing it bad again and they would see what they could find then.
Anybody got any ideas????

Thanks

Have you tested your fuel presure?

I dont know for sure if they did or not. I will call them today and find out. IIf they didnt, I will check it myself and find out what it is.
Will let ya know...