2005 jimmy p300 code

[redneck01]

I have an 05 jimmy with 260000 km on it i have owned since new. the sunday just passed i was headding down the hwy at 130 kph and the truck died. i pulled over and looked under the hood to find the air cleaner hose disconected. i tried to restart but nothing it would just turn over, at one point i thought it might start but nothing. towed it home and replaced the coil and distributer cap and rotor and it fired right up. today was the first time i tried to take it to work and as soon as i got on the hwy and it got up to running temp it shut down but not totaly. it wont get up over 80kph and it takes a lonk long time to get there. i got it home and hooked it up to my code reader and mass flow problem came up so i changed the mass air flow censor as well as the ignition modual as well as new set of wires. but it still runns bad and cant revi it up over 3000rpm, even in nuteral. hooked up the code reader again and i get the p300 code for random missfire. also upper and lower rad hose were sucked flat. had to open the rad cap to get them back to a round shape. I have been hard on this truck like everother chev i have and this is the first problem i have had with it. any ideas on what is going on? i am thinking intake gasket but it just stoped running at hwy speeds and i dont think an intake gasket would do that.....

[RyanbabZ71]

no ned for the same topic in 2 locations be patient someone will chime in