1997 Jimmy Won't stay running

Had a power loss and wouldn't start again. Mech. checked and had pressure and spark. New fuel pump installed and will run for 30 sec. then cut off. Each start, it does the same thing. Could it be a electrical problem, and where

Does the SES light come on? Are there any DTC's stored? What were fuel pressure and leakdown results? Ignition switch is a very common problem on 1997 also.

All are ok, but it just loses powerand stalls after 30 or 40 sec. and will start and do the same thing over and over

Classic symptom of lack of fuel flow or fuel pressure. Fuel delivery and ignition are not directly monitored by OBDII, that would explain no SES light. Have you checked the fuel filter?