Sounds like the MAF or the wiring to it is suspect. If the MAF is not working it will do all kinds of strange things. I'd start with removing the wire connection to the MAF and testing for proper voltage and make sure the wires aren't cooked. If voltage is good there then I'd start with trying to clean the MAF with the correct cleaner (NOT brake cleaner). If the MAF is shot then pick a stock one up from a JY and throw it on.
All those parts you mention sound like normal maint. items to me. I have a 2000 GP also and they will keep running just with normal maint. FYI, I have 488K on my GP and it's my DD. The only thing that does not work is the parking brake. I wouldn't throw in the towel on it at that low of mileage.
