94 s10 blazer 4.3 cpi

It's still beeen cold around here but details are:

Starts up great cold. after warming up and driving for awhile when at a
stoplight it shows the oil pressure dropping to about 10 on the dash
and it idles rough(if i put it in nuetral it's not as bad). runs fine
otherwise.This problem started off slight and has since become more
noticeable.Howevre as soon as you barely touch the gas it goes up. When
driving the pressure goes up to 40 or slightly above(where it's always
been).The car drives fine when moving
If you turn off the car it will start great again for the next ten
minutes after that it takes a bit to get it started. If i give it a
little gas it starts quicker.
Also this winter it seemed the alt upon starting was at like 16 volts
and then after awhile it comes down
I had the sulpher smell sligtly last summer and earlier this year.
Oxygen sens is original.cts replaced this summer. Another thing i
noticed is that running the car for three minutes i can't touch the
pipe before the cat but after the cat the pipe is still almost/is
touchable. I've smacked the cat but don't really hear it rattle.LAst
emission check my hc's and co was up.127 for the hc at idle and .10 for
co % at idle. Numbers dropped significantly at 2500 rpms

I'm thinking
1. bad cat  since the problem has gotten slowly but progressively worse
2. stuck egr
3.CPI is leaking have to go buy a 30 torx and peek inside

Oh I'm not noticeing any real heavy duty gas smell from the engine bay
after running or starting up. If i rev the engine there's a stumble
when it comes back down.No codes set.I did find the vacuum tube from
the air filter to the engine was off/put back on but no difference

Sorry about the length but try to be accurate. Any ideas?

Thanks
Mike