CHECK ALL GROUNDS! It is VERY possible during the pump replacement that one or more of the grounds that attach to the intake manifold are not making good contact. CHECK and CLEAN all four battery battery cables (both ends) and the terminals. Pay CLOSE ATTENTION to the two sandwiched Positive cable ends on the passenger side battery side post! Between those two ends there is a lead "bead" (looks like a 3/8" cable ferrule) that goes between the cable ends in a sandwich and that the terminal bolt passes through and when tightened, crushes and flattens out to ensure good electrical contact betwen both ends. It is essentially good for only a couple of uses, then flattens out so much that it just doesn't make very good contact. When that happens, a couple of thing occur (all bad).
First, you are now getting much higher resistance/no contact between the two ends - which usually means much reduced amperage flow (voltage will be fine, but current flow drops significantly) through the cable to the starter positive terminal. This will give you slow/no cranking .
Secondly, you will see the voltage gauge needle either jump all over the place when the engine is running, or reading a few volts lower - which might make you think that your alternator is going out - when all it is is a $3 O'Reilly's Auto electrical part that they HAVE to look up in the parts catalog as it wasn't on the computer system a few years back when I had the same thing happen to me a couple of days after two new batteries were installed. Slow cranking, when it did finally fire off, driving on a bumpy gravel road my voltage gauge the needle was everywhere. Traced it down to that little lead spacer.