Sounds like an electrical glitch of some sort / intermittent connection. Was it wet the day you experienced loss of transmission?
I don't think the alternator is bad. It should last more than 45k miles. At least 100 - 150 k (at least if it's new).
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TMS underdrive pullies - Stewart WP - PSS9 - Beisan Vanos seals - Zimmerman cross-drilled & Akebono Euro - Deka 649 MF - 55w HID headlights - 35w HID foglights - Hualigan double din - ACS (rep) alu pedals - Euro central storage console - Breyton Magic Racing staggered wheels - M5 bumper - M5 steering wheel - Tint
Stable: e39 M54, e53 N62 & Tribby