You asked only about words ending in "eep". Confer, however, with other words with the exact same sound, which are regular in construction:

reap, reaped, reaped, leaping
leap, leaped, leaped, leaping ("Leap" used to have the past and past perfect form of "lept". You still occasionally find "lept", but it's going away in favor of the regular "leaped".

What's the difference? Damfino.

Dave Oesterreich