4.3 vortec V6 running terrible

[straight6chevyguy]

Hi guys, been working on another project truck I picked up. It's a 2002 Chevy S10 4x4 with the 4.3 vortec and automatic transmission.
It starts and Idles fine and reves fine for the first couple minutes or so but after that and you give it some gas it runs really rough. it will rev up but is misfiring really badly.

I had trouble codes for maf sensor and O2 heater circuit malfunction.
I replaced the maf sensor but no change.
On my scan tool the O2 sensors seem to be working.
I have checked the tps and it checks good.
Also got a code for random multiple cylinder misfire after revving it a bit but disconnected the battery and came back today and it's gone ran the truck a bit misfire code has not came back. May not have ran it long enough I don't know. Funny though I drove the truck home and never got a misfire code until I ran it the other day.

Fuel pressure is 50-60 psi
I have also tried a new distributor cap. It also has new spark plugs.

I have done a little research on other forums but haven't really came up with anything other than what I've already checked.

I'm hoping someone here with more knowledge then me can point me in the right direction as what to check next, as I'm kinda lost at the moment.