Just to be certain, you're running FSX Accel, and want the latest confirmed version, or the latest BETA version?
Needless to say, the Beta version isn't perfect yet.
Anywho, you can find the latest, non-beta version, V18.3, here:
https://drive.google.com/open?id=1wpfjdjyaaLfuDdxOMk7VLdVrG0koa2jM
The BETA version, V18.4, is here:
https://drive.google.com/open?id=1Qn3y2uldzgZrPJbth2uW9S5GlgrBiykh
If you have TacPack, I'm currently working on adding AGM-88 HARM missiles to it. Mainly working on the fine details, now. I have the missiles on the plane, and they can be fired, as long as you're pointed somewhere near the SAM site that's painting you. Now, I'm working on the MFD pages unique to the HARMs, like the automatic Pullback mode, where if the plane detects an active SAM site painting you, it selects HARM missile, regardless of whatever else you may have selected, so all you have to do is fire one or two off to protect yourself.
Fun stuff like that. Not super easy for an XML tyro like me, but it's coming along
Like I mentioned, make sure you're not flying in a dense scenery area, or an area with a complex, high-CPS usage, setup. A lot of add-on scenery can really load the CPU.
Same with 3D clouds. They will eat FPS faster then nothin' else.
Finally, make sure you don't have a lot of background apps running.
A 3.5 GHz processor is a bit slow, but should do the job fairly well, as long as you don't load it up too bad. You can try locking your FPS at 30, also. It often helps the CPU by making a lighter load overall for it.
Hope something in here helps a little...
Pat☺