EGT3 strange behavior

I have a 916 Is engine on my Sparker plane. The plane/engine was new when I started flying it in April. I now have 93 hrs on the TAC time (120 hrs on the Hobbs time). I have been cruising at 70%, 75%, and 85% power settings. Lately it has been mostly 85% power setting, trading off going faster for more fuel burn. Temps were ok. About 15hrs engine hrs ago, I started noticing large temp variations on EGT3. Instead of holding steady at 1640-1650F, it started varying sometimes by 50-60 degrees. After a few more flights, it started reaching 1710-1715F at 85% power. All other EGTs remained at their previous EGT levels. If I dropped power back to 70% EGT3 dropped back in line with the rest of the EGTs. Going back to 85% power would then be ok for 10-20 minutes then again it would spike up to 1710-1715F. 

Because of this behavior, I started looking more carefully at logs and noticed that the peak EGT temp on takeoff power had been constant for a number of months but recently EGT3's peak had increased to about 1710-1715F. After a few more flights, now EGT4 is also around 1710-1715F on takeoff. Something is changing. 

I have discussed this issue with Dean at Lockwood Aero several times. He is helping with the debug. First comment was that EGTs are still below the EGT limit of 1742F. That's ok but I am not satisfied and want to understand what changed and what, if anything, I can do to improve it. He suggested an action of swapping the LaneA vs LaneB connections to the EGT3 injectors and running with LaneB off to see if the behavior was different (LaneA still enables EGT temp displays). This made no difference. 

Once we saw that EGT4 was also changing, the second recommended action was cleaning the spark plugs. We did that yesterday. It appears to have made some minor difference - EGT3 was not getting as hot at 85% power as before the cleaning, around 1690F vs 1710F at 85% power, but peak EGTs on takeoff power were still 1705-1710F for EGT3 and EGT4. I did not notice the 50-60F variations on EGT3 as I had before but it has only been one flight so far. 

I am attaching two figures to help with understanding the situation - the peak EGTs on takeoff history and the EGT3 temp variation. I am hoping for suggestions as to the next step. Thanks for the help.