1997 Z-71, 5.7 vortec. Let truck sit for 3 days. When started up, idled rough. Take off is slow. changed plugs, no good. what next?

misfire spark plugs coils wires did you wash engine water gets in under the intake to the plugs first if with a scanner check codes p0300 change plugs p0301 or 2 or 3 or 4 its one of the cylinders i would try just changing all the plugs first and start from there

Sounds like the chock needs a little TLC.

two things pop to mind with this truck, first these motors are notorious for having bad intake gaskets take a flashlight and look very carefully around the valley of your intake/block-head seal you'll possibly see either antifreeze leaking or a weird looking whitish or greenish sort of foam you can also use propane around the seal and look for obvious idle changes, I have done tons of these intakes in my shop, the other two things I would suspect if that looks fine are 02 sensors, or maf sensor.

run fault codes and look for a fuel supply sensor/servo failure. The heat is affecting the fuel system and is causing a fuel vapour lock or is over pressuring the injectors.

Sounds like fuel problem to me?? Have you changed the fuel filter ?

You are right this is a classic MAF problem or rather the air mass meter AMM which is the MAF working with the closely associated intake air temperature sensor IAT(a little bead like thermistor on wire sitting close to the MAFF in the air stream). The ECU was getting poor information from the MAF. The ECU had to rely on slow input signals from the IAT and feedback from the oxygen sensor on the exhaust to keep the engine running. The ECU hunted for the right mix, first rich and then lean but never settling hence the 'surge and slow' of the engine revs. When you disconnected the MAF you also disconnected the IAT and now the ECU had just the one signal from the oxygen sensor to depend on and so now provides a slightly rich mix giving the rough idle. You have done the hard work just change the MAF and IAT assembly.

I AM LOOKING AT TIMING ISSUES OR INTAKE MANIFOLD LEAK.OR EGR VALVE STUCK OPEN.

Do you know if the plugs were changed, a bad or broken plug will also cause rough idle and slow acceleration?

Could be the Idle Control Valve?

HAVE THE COOLANT TEMP SENSOR CHECKED TO SEE IF IT IS FUNCTIONING PROPERLY.HOPE THIS HELPS. BEST OF LUCK. LET ME KNOW?