As I have a 4 cylinder Jeep and an Air Cooled VW, I know exactly what you mean.I like the 4 cyl for in town driving, it reminds me of my old underpowered Volkswagen that you really had to use the gears and keep the rpm's up. On the highway the 4 cyl gets along OK but it's just too much work to try to maintain a steady speed when you get over 60 mph. Head winds and hills are tough on it. The stock gears are 4.10's and with 33's 4th gear ends up close to what 5th gear is with stock tires so you will only use 5th on down hills or drafting semi trucks.
I also have a 3 speed auto, and it is so underpowered. I'll get it up to 65, but that's about it.As I have a 4 cylinder Jeep and an Air Cooled VW, I know exactly what you mean.
However, I have a 3 Speed Auto, and it's a pig. It'll do 70, eventually.