1996 Chevy Astro - 4.3L

OK so there is a lot to talk about here, so here it is.... My dad has one of these vans and it recently died. The fuel pump stopped working.

We replaced the fuel pump, but even though it was replaced it still wouldn't turn on. For the purpose of testing we jumped the fuel pump relay, and now it is always on while the key is on (again just for testing).

The Check engine light is on and has been giving the error P0118 and P0123. P0123 is a TPS. We tested that and it did indeed seem to be bad. We replaced the TPS and are still getting the error, even after erasing the code.

We started the van and the van runs PERFECT for exactly 40 seconds. After 40 seconds it starts missing REALLY REALLY badly for a variable amount of time and then completely dies. In order to get it to start again we need to shut the key completely off and start it back up, and again it will run for exactly 40 seconds.

Any ideas?