I would suggest looking how the ball rolls through the pin deck and not what you're leaving.  If your ball is splitting the 8-9 every time, I'd find it hard to believe you're leaving lots of 7 pins.  While your ball may not be rolling out, it may be losing energy quickly and as a result deflecting.  Watch where the ball goes and you will find your answer.

So, last night was a rough night with carry.  After the night was done, this topic came to mind where the issues with carry were similar.  I was watching PBA bowlers, and numerous other great bowlers, leave numerous corner pins.  It didn't matter what they did.  But since I don't bowl this league all the time (first time this year) I wasn't stuck throwing the ball in the normal place.  I looked at the shot with a fresh mind without any preconceived notion of where to play.  I did have better carry than others but I can't say I threw the ball great.

Long story short, it appeared the difference between those who carried well and those who didn't was where they played the lane.  Had nothing to do with type of ball being used or release type, though straighter bowlers appeared to do well. 

Sometimes what is necessary is a set of fresh eyes on a shot to help determine where changes can be made.  We are all guilty of walking into league and expecting the same shot as the week before.  We get out the same ball, stand in the same place and throw the ball the same way over the same mark.  And when things are a little different, we can't fathom why we aren't scoring our normal scores.  What I would do is start fresh.  Perhaps start off targeting a different line or using a different ball.  Do something different and then go from there.  It is difficult for anyone to know what you are going through since we aren't there.  How does that saying go....

Insanity: doing the same thing over and over again and expecting different results.

Albert Einstein

Speed certainly can have an effect, lower speeds don't result in as many hits where the head pin comes across the lane to take out the 10 pin.  Try adjusting your shot to come in a little lighter than a "solid" strike.  Not the shot that leaves a weak 10 pin, just a little lighter than that.  Sometimes that will carry when the solid ball won't.  --  JohnP

I am a stroked throwing 14 pound balls with the same ball speed as yours. When I was throwing 16, I got much better carry and did not have to be as careful about ball selection. With 14, ball selection and resulting entry angle is much more important.

With 14s I see blower sevens on what seem to be solid pocket hits. In reality, the ball is coming in to sharp and hitting slightly behind the head pin.

Ringing I ten pins on what look like solid pocket shots are actually too high shots.

Also, I leave 8 pins on solid pocket hits when I move in deep. This tells me that the ball rolled out or deflected so I adjust accordingly.

It's not luck. It's understanding what your ball is doing and then making the right decision about how to fix it.

Trust what you see and feel that you need to do to fix what you see. Make the adjustment and then adjust off of your adjustment if necessary. You have bowled a long time so I know that you understand that you bowl best when you follow your own "feel" and get comfortable.

I think Rico nailed it.  Even with a slower ball speed, don't be afraid to use a ball with more surface.  The ball needs to stop hooking and start rolling as it enters the pocket.  If the ball is still hooking as it enters the pocket, the ball is still sliding and not rolling