Hi - I noticed the Hauler runs pretty hot, and I would sometimes get into a spot of bother when arriving in a system. I was too much of a skinflint to upgrade the power plant, so what I would do on a multi-jump journey is this: as soon as I jumped into a new system on my route, I'd untarget the next system in the route, exit super cruise, let the FSD and the overall ship heat level cool down briefly, and then as soon as the ship heat was down to about 48% - 50%, I'd hyperspace to the next system (you don't have to retarget the next system on your route, as if you have a route plotted the next system is retargeted for you when you exit SC), and then repeat this each jump until I reached my destination.
I would add that although I was too tight to upgrade the FSD, I had a class B power distributer, which helped the FSD cool down very quickly, and probably the other systems too, so this routine didn't add too much time to my journeys. If I had been looking at keeping the Hauler for longer, I'd definitely have upgraded my modules to try and sort the problem out, but I didn't intend to be in the Hauler for long so I just put up with this work around, and now I have sold it for a Cobra.
If I needed to stop to scoop fuel, again I'd untarget the next system so that I could drop out of SC as soon as I'd turned around and moved away from the star at the end of scooping. Also handy to be ready to drop out if any ships are looking likely to interdict you.
As I said, this was all a bit of a pain, and if upgrading your FSD sorts you out, then that's cool (pun intended), but thought I'd offer an alternative just in case you don't have or want to spend the credits right now.