How reliable are the 3.8L engine? They seem to have plenty of power and look like a small 5.2L/5.9L Magnum.
I bought a 07 Braun Companionvan in Feb, 08 to haul my handicapped sone around in with his wheel chair. It runs great, just haven't heard any long term good or bad stories. It now only has 4800 miles on in the 14 months that we have owned it.
My dad recently bought a new 08 GC SXT with the 3.8L 6-speed auto. That seems to be a much better transmission than the 4-speed auto in mine.

Hopefully, these 3.8L engines will last a very long time. I really wouldn't even worry about it, but with the future of Chrysler unsure, the Lifetime Powertrain Warranty is also not a sure bet either.
Both me and my dad are very pleased with our vans. Well, all but the constant brake dust. Will definately go ceramic pads when they get replaced!!

Here is a picture of mine. It is Magnesium Pearl.

 

The 3.8 is a very reliable engine.
What makes you thing the 6 speed is superior to your 4 speed?
From what I understand they are of similar design. the 6 speed just has the option of 2 different ratio 2nd gears and 2 overdrives. It depends on how you drive which gear is selected.
I wouldn't be surprised if the 6 speed has stronger components though.

 

My Dad's shifts 1-6, no second prime like the crappy 545RE in my 08 Ram. It keeps the engine in the sweet spot thru the gears when accelerating.
Mine (Grand Caravan) seems to hunt 3-4-lockup at around 40 mph. I usually just run in 3 around town.

 

Has your dad heard any low grinding sound from 1st to 2nd around 15 to 18 miles? If he has the problem is with the number 5 needle bearing. Thats only on the 62TE transmissions.

 

I have seen many 3.3's and 3.8's with well over 200,000 miles. The highest was 426,000 miles on an original 94 3.3. Probably one of the best engines Chrysler ever produced (s) I worked at a Chrysler dealer for 8 years.