jabez

Arriving at 12:30 you can figure that it will take you until at least 3 pm to be checked in your hotel. I'd do a walk around Piaza Novona, the Pantheon area, eat near there or around piaza Fiore. Or work your way down to the Spanish steps area-lots of good restaurants. It all depends where you are staying.
You'll then be wiped out and ready for bed.
Day 2 I'd do the Forum and Colosseum bright and early and then head over to the Vatican museum to arrive between noon and one. Should be no lines.
Then I'd do a "free tour" of St.Peter's and ,if possible a Scavi tour (advance reservations only).
I would then head back to freshen up.You might then do a night tour of Rome.
Day 3,your goal is to be at hotel by noon (get hotels OK), train to Venice.
Checkin and spend a day and a half in Venice.
If your ship leaves late , you could arrive in Venice on Day 4 and add another day to Rome.
Although I would try and spend all my time in Rome, I think I would at least have enough time in Venice to get a real feel for it.

HappyTraveling

I haven't been able to get online until today. WOW...and THANK YOU for all the advice. (I can't do without this forum

I'll REALLY have to reconsider my plans now. Will probably add 1-2 days to the plan. "Just strolling through Rome..." sounds so limiting. It's too bad there's such a thing as limited time off from work....

Thanks, ya all for the advice.