Without the IDS installed 6th gear would sound like a can if marbles much below 65 MPH and shouldn't be used in any event below that. It makes a big difference by installing it, however don't lug the engine much below 2300 rpm's in any gear especially the upper gears.
If I'm reading it right then at 30 mph I should be about 2500 RPMs. There are several towns around here where 30 is the speed limit a few miles. It seems to me that the engine is running hard just to run 30 mph. Is this right and I just need to get used to it?