after 4 minutes of warm up and few meters from the parkway the engine try to shut off momentarily and resumes its normal course. This failure is not constant

 

And it only happens after a 4 minute warm up and a few meters from the parkway?
You posted in the "Ask GM" section. Do you really think GM cares how a car that is 16+ year old runs?
We need a better description of your problem, and what you have done so far to figure it out.

 

the car had engine modifications, now have 383 LT4,292 xfi cam, 36 LBh injectors, PCM tuned, MSD distribuitor, 1-3/4" headers, airgap intake manifold,
the problem only occurs at the beginning of the trail, a few meters outside the park, the engine makes as if it were off

 

have you had it scanned for trouble codes?

 

Mechanic is the only person that can tell using the the Cpu