Another powerlevelling question

So if I do powerlevel a friend to say lvl so he can join me in my TVHM game, will he get credit for the quests he does with me?

Meaning will it screw up his quest line when he beats normal and wants to do TVHM on his own?

No, he’ll be asked if he wants to skip the quests before them when he gets to them. So if he’s already made it to Sanctuary, he won’t have to do the prerequisite quests.