Hi Closer, welcome to SMF, I'm a new MES Sam's 40" owner too, as well as recent newbie on SMF.
Like you, my 1st cook was 6 racks of baby back ribs, I was proud to be able to lay those babies flat two to each rack in the MES 40.
Like you, I had trouble getting up to temp. My problem was an extension cord. I had a 50' 14 ga. cord to get some distance between the house and the smoker, so smoke wouldn't drift back into the open screen doors/windows. After several temp resets, and a couple of hard resets (1st put MES digital control in off mode, then unplug the power cord wait, plug in cord and turn on MES control and set it), I then moved the MES and plugged directly into my house outside outlet, "no extension cord". PROBLEM SOLVED! The MES came right up to temp 225. The ribs came out great, even though the MES spend almost 3 hours at 190 before eliminating the extension cord.
I will say I have had the problem once since, but I think it was due to using cold water in the water pan instead of hot water. I used the MES last monday, smoked a couple of whole chickens and the MES performed great. I will be trying it later today with a couple racks of ribs, a couple of chickens and may some other treats.
One thing I noticed, I use a digital thermometer with remote probe - thru the top vent, probe either on bottom shelf or 2nd shelf up. The July 4th smoke, 10 racks of ribs, I had problems getting to temp, I assumed cold water. My digital taylor was reading 255 to 270, and the MES was reading 160-180, hmmm. So I opened the hatch and the remote probe inserted thru a chunk of potato, had fallen and was resting against the inside wall about 2" inches above the heating element/wood metal cover. So the cabinet was getting heated fine just not the inside air. Maybe I should have closed the top vent slightly, not really an option I want to try, worried about smoldering wood that gives off too strong of smoke with vent closed down. Another thought was the element is making contact with the cabinet, any maybe should be insulted from cabinet, not sure I will call Masterbuilt later today about this.
Not sure if any of the above helps.
Enjoy your new MES!