When I came home yesterday the landlord was in my driveway working on something at the neighbor's house. So I had to park in the yard. I used 4 HI so that I wouldn't tear up the grass. Well I didn't realize that I had left it on until I got to work this morning. I only drove it about 4 miles and I only got up to maybe 55mph at most. Will this hurt anything?

 

My opinion: you put some wear on the CV and U joints as front and rear are not synched so on pavement the "being out of synch" slip has to be taken-up by something and that is the CV and U joints. The T case probably took some additonal wear as well.

Be sure to listen for any clicking or clunks next time in 4wd.

 

I just went home for lunch in 2 HI and everything seemed to be fine.

 

I drive around in winter in 4wd a lot at speed and haven't hurt anything that I'm aware of lol!

 

In 2Hi the front CV joints are not under any type of load, same with the T-case...so would expect all to be fine.
Probably nothing to worry about.
Next time you have an opportunity to go off pavement and into 4wd for a short distance: just do some stops and gos, slow turns and listen for any clicking noise or clunks when taking off from a stop. Slow take offs and stops, turns.

Again probably nothing is damaged.