Need input on a few questions on the Explorer Sport Trac.

QUESTIONS
* What year was the Sport Trac upgraded to I.R.S.?
* I've seen an 01' advertised with I.R.S. Did Ford recall and upgrade straight axle leaf springs to I.R.S.?
* Is the 4.6 V8 a decent/good engine or is the 4.0 preferred?
* Was the 5 speed manual ONLY available in 1st gen (up to 2005)? With V8?
* Was the door lock combination pad available on newer Sport Trac bodies?
* Aside from the obvious (age/miles/wear/rust), what year and model could be considered the best/most reliable etc... & why?
fictitious example:
stay away from the V12 they blow head gaskets, the inline 6 is know to be trouble free 500k motor

thanks in advance

 

Any interest in these anymore?

 

We loved ours. 4.0
If you get a Gen 1, I have a nice cover for it. We only used it a few times.