The vehicle is a front wheel drive with a 5 speed transmission. It just recently started jumping out of 5th gear when going down the highway. This does not happen all of the time and it seems to happen when you let up on the accelerator.

If you are talking about driving along on the highway, mashing the accelerator, and having the transmission drop down to the next lower gear, then that's correct. It's supposed to do that. All vehicles with a standard multi-gear transmission will do that. It allows the engine to operate at a higher speed. The faster the engine speed, generally the more horsepower it produces. It also changes the ratio of engine speed to wheel speed. The faster the engine is going in relationship to the tires, the more torque, or pulling power is applied at the wheel. This combination allows the vehicle to increase speed faster. If you're on the highway and need to pass someone, you don't want to take forever doing it. That becomes a safety issue. You will also see the same thing happen when pulling heavy loads or going up hills too. It gets the engine into an optimal operating zone to maximize horsepower and torque.

What speeds, does it make more noise in 4 wheel drive or the same. There are several possibilities, need more information. Does it howl in all the gears or in 5th gear only.

Sure you can, It just makes the engine work a little harder. As long as your not running down the road at 3000 rpm's all the time, it will be fine

chek your selector locks and synchronizers for number 5

You don't provide much information to go on (type of vehicle, type of engine, 2wd or 4wd, etc.) RPM is always going to be based on the speed you're traveling with a standard transmission. My 4 cyl 5 speed Nissan pickup in 5th gear runs at 3000 RPM at about 75mph.

sounds like the shifter linkage has worn and not working properly need to lift in air and inspect the linkage

indicates a TCM problem
run the fault codes to determine the exact problem area

Either you have a worn shift fork and fifth is not fully engaging or the synchro for that gear is worn Both are internal and if fork is worn I suggest you have synchro replaced as well..

IF GEAR SHIFT SHAKES THEN THE TRANSMISSION MOUNTS COULD BE BAD. HOPE THIS HELPS. GOOD LUCK

Sounds like your pressure silenoid is going out in the transmission. This controls when the vehicle shifts