purchased in fall - only ran to test drive... picking up in a week - concerned!!!

1990 comp ts6m
351w
1:1 I think
prop unknown - has spare

problem I have is during the test drive - 3800 rpm WOT and 38 mph was the max!!! I need more... hole shot was strong so i'm hoping I can change prop and gain a little top end but my concern is the wot at 3800 rpm seems low for a 351w...

I understand there are A LOT of factors that could effect this including but not limited to - bad fuel, dirty carb, bent prop (was so excited I was buying I never even looked - my bad) low compression (ran smooth) - what else could it be??? wrong prop size? best stock prop suggestion (what should the prop be???)