The A154E is quite reliable. The MA71 version is a tad bit beefier than the MA70 version, so if you're swapping one in get one out of a MA71 chassis.
While an automatic transmission is almost always heavier (as it is in this case: a little heavier than the R154 and a lot heavier than the W58) it shifts faster than you can.
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In a very high power build automatic transmissions are my preference... for general driving, I prefer manuals.