Golf killing me at the range

Went to the range last night after making some changes to my swing thought. I realized I wasn't dropping my right shoulder.
Took a 8 iron and 6 iron and got 90 balls or so. I went through maybe 60 with the 8 iron. Maybe 10 of those were 'bad' shots. All the bad shots were short as I skulled the ball. However, the good shots were freaking sweet. I was dropping them around 130 to 140 yards with the 8 iron. Rolled out to 150 to 160 for a majority. I was stoked. This was a 20 yard improvement from several months ago.
In comes the 6 iron. I am thinking I can drop it around 160 to 170 and roll out to 180. 200 is where my driver lands, so this is massive improvement. No dice though. 6 iron was dropping 120 yards, with roll out to 140. I couldn't hit a 6 iron farther than my 8 iron. I thought I was crazy so I went back to the 8 iron. 140 yards, rollout to 150.
Swing changes after ingraining bad swings for two years is a tough thing to do. I am not getting my hips around in time with my shoulders. Still trying to 'arm' it through the ball.

Next trip, I am going to slow down the swing. I would be happy with 8 iron to 140, and 6 iron to 170. Will see how it goes.