no they would be the same. for example, if you let a magikarp get to level 99 and evolve into a gyarados at level 100 (why would you ever do that
) its stats would jump up something huge!
a word of warning though, endure/reversal is a risky strategy with slaking since it only moves every second turn. with 1hp left your a sitting duck on the truant turn. unless its ingame and you can switch every time you defeat a pokemon. if youre doing it for breeding (eg to get a reversalken) you can just use the vigoroth.