idles fine; stalls under load at 2K

[aintmisbehavinn]

Murphy is giving me hell. Just started 72 GMC truck with rebuilt original motor 35K miles that was in storage for 8 years. Plenty compression, no knocks or ticks. Tank drained before storage, pick up cleaned, no clogs in line, new fuel pump, holley 4150 dual pump rebuilt with no leaks, bowls adjusted idle perfect with small torquer camshaft. New ACDELCO cap and rotor on MSD OEM replacement distributor with MSD 6A box. New MSD wires and ACDELCO plugs. New fuel filter, pump and lines. Fresh 93 octane gas. Truck ran perfect daily for 2 weeks then began to stutter at 2 k when warmed up. Occasionally stalled but restarted immediately. Truck now will not rev under load over 2K however will rev to 5K at idle. Beginning hard start on 180 temp. I have changed everything but cannot figure out why it only stalls under load. Does anyone have any suggestions where to look next. Timing is dead on and advancing properly, the only thing I haven't changed is the coil; alternator seems to be working properly according to the gauge. What would cause it to sputter and stall over 2K under load? Truck ran perfect before storage and shortly after. Just getting worse. Don't understand why it would idle perfect, rev perfect, soon as I hit passing gear motor just drops like a rock. No change after fuel pump and carb rebuild. No leaks except for trans pan overnight.

I'm wide open and running out of solutions.