My mechanic, whom I trust a lot from prior work just had my tranny (4HP22 EH) sent out for rebuild, however he is not specifically familiar with BMW's electronics. The tranny's back in car and everything seems very good, smooth changing, strong pull, etc. except for 1 intermittent problem. Occasionally, when it's shifting up from 2nd to 3rd, there's a brief (half to one sec)hesitation, the engine revs up "freely", then it shifts up. Any ideas what to check first ? Is it likely to be the tranny itself, or TCU, sensors etc.? Thanks again in advance, for your help.