I'll let someone else with a Series 2 L67 and 3.4 answer your plug question (but it sounds to me like the NGK TR55 would be great).

As far as a trans cooler is concerned, it'* only reccommended on the 4T65E when doing towing or alot of mountainous summer driving.

The 4T60 is a different story altogether. They benefit from one in nearly any situation, but can be overcooled if you're not careful.

Autolite 605'* gapped at .055.

Hey!! Some one hijacked my post! Hehehe

My dad and I agreed in something. He should not argue me, or he will lose. He took the car to a mechanic who has a very decent code scanner. He initially thought could be the coils (eventhough I told my dad why they wern't bad), but the scanner found a misfireing cyl #6. He moved the cable away from the o2 sensor and the problem was temporarily fixed. He erased the code from the computer and charged my dad only $10.
Dad told me the car was running good again and he was going to buy the cables latter today. And I told him I was going to thank you guys for the help and for being so precise, eventhough we ignored my recomendations
I will take it for a test drive on the weekend to see if she got back her "mojo"