Hi guys...

I drive 80mph on I-25 near Albuquerque every day commuting...my '85 300DT does, what, 3400rpm at 80mph?

I'd REALLY like to lower those RPM's...I've read a couple threads here, but I haven't seen a reference to:

1) exactly what rear end part I need and where and can find it, and
2) how much $$ that part is, and
2) about how long/hard it is to do the swap, or
3) about what a Mercedes mechanic would charge to do the job.

I'm looking for pretty much lowest possible RPM's, but I'd go a little higher if that prooved beneficial in some way.

Thanks...