87 740 GLE

This car has recently come out of 4 months of storage. Just replaced the main fuel pump, and pre-pump appears to not be working (along with gas gauge). Additionally, when I start the car after it's been sitting for a while i run into several problems:

1. Car will usually start right up without multiple crank attempts, but is initially sputtery and takes a few seconds to smooth out.

2. Regardless of how long the car idles before being put into gear, once I either put it into reverse or drive, the car dies 90% of the time. It might do this a couple times, but then it drives fine once it starts. If the car does manage to not die when put into gear the first time, it drives terribly for several minutes (even after the engine is fully warmed up), almost like it's only running on two cylinders. It very well may be on only two cylinders for all i know.

3. If i rev the engine in idle before driving it, it sputters around at 1750rpm. No higher, no lower.

I've also been getting horrible mileage. Approx. 17mpg city. I used to average at least 25. I'm planning on running some injector cleaner through it and perhaps clean the throttle body this weekend. I'm also going to do some work on the pre-pump when the time/gas level is right. The main pump I replaced was after-market (closest OEM was in St. Louis for some reason). Wondering if maybe the check valve failed. Don't know what recourse I'd have with this aftermarket part. Might make sense that the main pump is running poorly, as the pre-pump isn't running at all.

Also wondering if this is an FPR problem. My exhaust doesn't smell rich, and I don't see any smoke.

It seems like my problem fits into a lot of the categories on the FAQ, but doesn't specifically resemble any one of them. Any ideas would help...

thanks
-scott