Yep. Wasn't very many years ago that the regular timing was well in excess of 5 hours.
1974 electrification introduced a 5 hour "headline" timing, but there weren't many services and many of them took longer:
1M18 07:10 Glasgow to Euston 12:29 5h19m
1M25 07:15 Glasgow to Euston via GSW 14:03 6h48m
1M05 09:10 Glasgow to Euston 14:29 5h19m
1M30 11:10 Glasgow to Euston 16:28 5h18m
1M19 13:10 FO, dated Glasgow to Euston 18:18 5h8m
1M35 14:10 Glasgow to Euston 19:17 5h7m
1M46 16:10 Glasgow to Euston 21:26 5h16m
1M52 17:30 Glasgow to Euston 22:37 5h7m
I expect there was a 5h schedule in the down direction, I don't have the timetable for Glasgow arrivals in 1974. Although there was a hourly xx.45 down departure "slot" it wasn't used every hour.
It's only been recently that there's been an hourly service, but that will presumably rely on traffic from intermediate stops, certainly in my experience the trains are relatively empty north of Preston.
EDIT GSW - Glasgow & South Western, via Kilmarnock and Dumfries. The 15:45 down service used this route also, diesel-hauled between Carlisle and Glasgow of course.