[Chevyman69]

Running rough usually points to an EGR related problem. Could it be when you plumbed the system it is constantly pumping in exhaust gases which would make a poor idle and poor cold engine performance. You did not say if it smoothes out in higher rpm or not but if it does I would check if the EGR is stuck open. Check the valve, you do use a valve when retofitting a Vortec right, and see if the diaphram is opening and closing and if it is open at idle it would explain the symptoms you gave.

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69 CST 10, 402, steel crank, heavy rods, Federal Mogul Forged Pistons, 9.9:1 compression, polished ported 781 heads 2.19/1.88 manley stainless valves, Crane Powermax Hydraulic roller 288/296 and .587,.610 lift, hardened pushrods, Crane Roller Rockers, Weiand Action Plus, 750CFM Edelbrock QJET, MSD HEI, MSD 8MM Wires, should be about 500 H.P. 700R4 2500 stall, pretty nasty shift kit, 373 Auburn Pro Series Posi, buckets/console air/tilt/tach 4wheel discs
Daily Driver: 92 Chev Reg Cab LWB Silverado 4x4, loaded, 350 Accel filter/cap/rotor/coil/AC Delco RapidFire plugs, Edelbrock intake and headers, true duals 700R4 with B@M Shift Kit for now!