mighty max has problems at 65mph

[joeyb4x4]

hi guys i have a 1984 mighty max with a 2.6 it runs great at idle has plenty of power its been rebuilt by me and my dad two years ago. my problem is ill get on the freeway truck will run great i can go 70 75 no problem all of a sudden it will start sounding like i have a cold air intake on my truck and im currently running the stock aircleaner and housing i checked my fuel pressure i have 3.5 pounds running the mechanical pump still. for my ignition i have ngk plugs i put in 1000 miles ago and brand new ngk wires put on two weeks ago brand new cap and rotor. thought the coil might be causing my problem but ohmed it out and tested fine. when this problem occurs at 65 mph its miss fires on every cyclinder i put the clutch in and rev it up it stilll miss fires but out of know where i bring it back to idle for a minute and free rev it again and it runs great truck runs cool on temp just replaced fuel filter also if you can help me please let me know im in need of help to figure this out and it doesnt happen all the time some times its fine others its not my number is 12093511511 you can reply on the forum and ill check it or iff you want to txt me or call me would apperciate it so much thanks for all you help joe

[camoit]

sounds like an emission problem. PCV valve not working correctly or some other vacuum leek.

[pennyman1]

check the evap canister and associated hoses. also check the bolts holding down the carb and the intake and exhaust manifold - leaks here can cause imtermittant problems too.