new spider assembly? the updated one?
If you bought the multec-2 upgrade, you should have got the new fuel pressure regulator and installed it.
I assume you installed the new FP regulator.
Maybe your fuel pump is acting weird...
tough to give you decent advice on something like this. check your connections on the fuel pump( difficult, I know).
FWIW my 98 Tahoe started the other morning and ran like dog sh!t for about 5 seconds...no idea what that was from. no codes, nothing. who knows