EDIT: Finger trouble...sorry, title should read T3 to T5 connection question...

Considering an ex Ireland return trip to the US which would have me trying out the new AA 777 (as a BA booked itinerary and codeshare) coming back form LAX to LHR with an onward connection to DUB but note the AA LHR arrival terminal is T3 and the BA LHR - DUB leg is T5. Connection time is 2 hours 30 minutes, as i've no experience with this AA flight (if it is usually on time or not) and tend to terminate at T5, can anyone give me some guidance on whether this is enough time to account for usual delays and change in terminals (and what would be involved in changing terminals please! I believe it is just catching a bus between them airside but maybe I am wrong?)

I could alternatively simply use the slightly later connection to DUB from LGW and happen to 'miss' that last leg (and then take the train back to BRS)...but ideally would take the flight for the TP's, avios and love of flying.

Any sharing of experience with this greatly appreciated ^ Thanks in advance.