What are you looking to do with your Jeep? I have had my 2009 3.7L for about a year now and I haven't had any problems at all. I am at 55K right now.
About 90% of the time, I have enough power, but sometimes when I mash my foot down, I wish I had a bit more power.
I would also take the 4x4 system into consideration. Do you want to tow or go off road?
Either way, I absolutely love my Jeep, so since you are looking to purchase a Grand Cherokee, you are off to a good start!
2009 3.7L Laredo Black | Two-Toned Leather | RER Nav/DVD/BA System | Viper alarm | HID's in the lows and fogs | Westin Brush Guard | Tinted Tails | Custom Blue LED Interior/Rear Hatch Lights | Rough Country 1.5" Spacers | General Grabber 255/70r17 -- Island Beach State Park 4x4 Mobile Sportsfishing Permit In -- To Do: Install Uniden CB, Rock lights