Ahakohda,
Temp swings have a variety of causes and may not even be temp swings, instead may be faulty measuring equipment. The MES is known to not have very accurate digital temp. Mine is about 15-20º off, so I use a digital Taylor with probe for cabinet temp, a second Taylor for meat temp, and a cheapy analog oven dial inside as a cross check. What is important is to monitor a couple of things and make notes. Keep a log of Outside ambient temp, MES readout inside cab temp, Taylor inside cab temp, Meat temp (except for ribs). During the first hour of the smoke check these every 10 or 15 minutes and jot them down. You can switch to every 30 minutes or 20 min for the 2nd hour. 3rd hour every 30min. Basically that first hour you are making sure the MES is doing what it is suppose to do, slowly raise temp of the meat. Make a note when it hit your set point temp, this is important because different outdoor ambient conditions will affect how fast the MES achieves set point. Also different loads affects how long it takes to achieve setpoint. You can compare your notes and understand how your MES works under different conditions. (Be sure to verify your temp measuring equipment with either boiling water or the ice method).
Since your in NY this time of year the ambient temp is extremely cold, that plus wind can play havoc on temps especially if you are in the habit of opening the door. One basic rule is "NO PEEKING", leave that door shut unless you need to foil or do something. Preheating is especially helpful in the winter. I will preheat my MES for 2+hours when it is cold 40º and under, 1 hour when 55º and under, at least 30 minutes if warmer than 55º. Preheating makes the the MES a very stable cooking platform, from my notes on many smokes I had noticed that after 3 hours of smoking recovery was faster. There is two reasons, 1st after several hours of smoking, everything inside the MES is heated up, including the racks, water, insulation, even the outside metal is warmer. 2nd the meat is now heated up, so instead of the meat being a heat sink as in the beginning of a smoke it is now stable and the inside cabinet gets warmer faster during recovery. Also rem. that heat always goes to cold, thus at the beginning of a smoke the meat is absorbing a lot of heat, different cuts or types of meat react differently so this can appear as a temp swing, because of the way it reacts with the heat. (Another reason to allow meat to come to room temp before putting in smoker.)
Your best bet may be to wait until May or June and see how your MES operates and then decide what changes need to be made.
My MES being the older model only has a 800 watt element, for Sacramento Area mild temperatures that has been fine, however recovery and getting up to initial set temp can take awhile especially if there is a big load in the smoker. My plan (dream plan, actual might end up different) is to add a secondary 300watt element so the heating will be 2 stage. Both stages will be activated initially to bring up to set temp faster, as the temp approaches the set temp the 300 watt element will drop out at 5º prior to set temp, the 800 watt will have no problem with the remaining 5 deg. If the temp inside drops 10 degrees the secondary element will kick on to assist the primary in getting back to set temp, again will drop out at 5 deg prior to set temp. I may include a data connection so I can control and monitor it from my PC or a laptop.
I will be rounding up the parts in May and hopefully have it done in mid June. I have been holding off on doing this remodel waiting for symptoms of wiring/terminal problems that are common on the older MES, which requires drilling out the rivets and opening the back. However my MES has worked great since day one, so I haven't fooled with it. There is no point in holding off longer, it would be preventative to do it before struck with the wiring problems.