99 Silverado 4.3 stuttering/starting problems.

[mseriously]

The truck is giving me more and more problems as of late...I have codes P0102, P0300 and P0420 showing up. P0102 is MAF code. Installed new MAF. New air filter. Noticed that previous owner cut out the bottom of air box for more air flow??

P0300 is the random/multiple misfire. This is probably because of the rough starting. It's specifically harder to start when colder and more so when it's damp. I recently replaced the intake manifold gasket because it blew out on the rear side (common problem), new distributor, plugs and wires to boot. The misfiring/stuttering while driving has been a problem for the past few years, so it was before the gasket blew.

P0420 has to do with the catalytic converter and possible o2 sensors...all that I've read says to deal with other codes first...

Any ideas? I'm going insane chasing this one down...basically it will start real hard, no stuttering, just turns over for about 5-7 seconds then fires off. Once I have it driving it will stutter and putter through the first 3 gears...but once it warms up it stops, and if it's warmed up it will also start fine too.

ANY ideas?