[vettestr]

Maybe first check should be starting engine in garage with hood up so you can see all plug wires. Do this in a darker area so you can see any misfires or voltage leaking from wires while running. Use a wooden stick to move wires a little so you do not get zapped but look for sparks jumping to any metal surface. DO NOT gas yourself in garage but a short test in darkness or do it at night in driveway tells a lot. Shorting wires will cause a stumble at loaded cruise RPM for sure.
Check the total timing, that is above 2500 rpm so check at say 2800 to be sure. Verify initial timing while you are there. I would look for numbers in about the 10 to 15 degrees initial and 35 to 39 degrees total. If you do not have a degree'd damper that shows 40 + degrees then masking tape and a mark the same distance as what is marked will get you close. An advancable timing light is worth its weight in gold and maybe a great reason to go get one now! I like the Craftsmen from Sears for bang for your buck.
You said it is a new install so verify coil polarity. Look for spark quality by removing the easiest to get to plug wire and put an old plug in it if you have one, then start with this wire and plug laying on intake so you can see plug fire. The color should be a neon blue, if it is a yellow or orange the coil is probably bad on a MSD system.
I have even money on it being wrong total timing or a bad wire or 2. Let us know what ya find.