Spins but doesn't fire.

My son drives a 93 Taurus 3.0. We put new head gaskets on it about six months ago. Started OK. Seemed to run OK around the neighborhood but he
never really tried to get out on the highway with it.
About 2 weeks ago he mentioned that it starts OK, but after about 3 miles it seems to lose power and barely pulls itself along.
Friday he drove to work and back. Saturday evening it would turn over but never fired. Plugs look OK. Lot's of spark. Sprayed some started fluid into throttle body. Started right up and idled for 4-5 minutes. Monday morning, it wouldn't fire. This evening it needed starter fluid again to start but then we were able to drive around the neighborhood without problem.
I'm thinking fuel pump and/or filter. Am I on the right track? Isn't the pump in the gas tank. How big a hassle is it to change out?
Fred. (Life is good, don't blow it!)

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