well mate from expeirience,you need to do what you feel makes you happy.
i was assistant manager in an accessory shop ,been there 11 years.then thought i need more cash so went to sell cars for ford.i was there 4 days then went back where i was cos i hated the job.it bored me,had very little interaction with people.didnt feel good when i sold the car and wasnt interested in it.plus the boss was a dick.
im back as assistant manager again and although the cash is shit i love the job and 98 per cent of the people i deal with.

i love cleaning cars but i wouldnt do it cos it would take the pleasure out of it for me i think.

what you need to do is weigh up if you need the cash,because possible promotion could get you lots in the future or if you want to be happy.