The 3.5 in that Trooper WILL work. Yes the later model ones are better but it WILL work. As long as you don't try and use a direct injection 3.5, you'll be fine. Just swap over your intake manifold assembly with all the attached sensors/throttle body etc. I believe the Trooper used a drive-by-wire throttle body assembly, that may be why they say it won't work, but if you use your intake manifold etc, you'll be fine