I will be travelling from Lahore to Abu Dhabi to Rome to Dallas to Manhattan KS. The flights are booked in a single ticket with my airline changing from Etihad to American Airlines in Rome. I wanted to know whether I'll go through pre-clearance in Abu Dhabi or will I have to go through Customs in Dallas? Secondly, when will I have to recheck my baggage? Will it be when the airline changes in Rome?
To your first question, preclearance only applies when you have a nonstop flight from a preclearance airport to a US airport. So although Abu Dhabi does have preclearance facilities, you won't be able to clear US customs and immigration there, since your next destination is Rome, not the US. You will clear US customs and immigration when you land in Dallas.
I don't know whether you have to recheck your baggage. Perhaps someone else can answer that, or else you can ask the airline.