anyone recomend descent leakdown tester?

well if this is another clue as to whats going on, i have a non lock up A-518 transmission and when i'm crusing down the highway in overdrive and i shift out of overdrivge smoke comes out my pipes after shifting out of overdrive.....It seems like whenever i'm in a high vaccum situation is when the smoke comes out the pipes. If uit's my valve guides i might as well just put new heads on the wish list, i'm just tired of playing the guessing game and want a leakdown tester to make absolute sure