TL:DR
Here's an overview of my main build:

Below are 4 optimized Minigun loadouts. If you're not sure what to pick, go for (Balanced)!
Explore and try the others to see which is best for you. Enjoy!

Be careful with this one. With the Lead storm Overclock you have no movement while spinning up the minigun. Jump before and after shooting to keep momentum and it'll help get away from bugs while you dish out DEVASTATING damage to bugs.

The Exhaust Vectoring Overclock is a good middle ground between ammo Efficiency and Damage.
If you're not sure which role your play style is better suited for, try this one out!
Just watch that ammo counter. With a base capacity for 2400 rounds, you may want to consider taking the ammo mod in row to of modifications.

Need as much DAKKA as you can imagine coming from a MINIGUN? Let's get this one started up! Spray at Glyphid munchers all day because you'll be cooling your gun each kill. Find a good position and don't let them get close!

This one is a clean overclock that is surprisingly effective! First of all, the accuracy is incredible for taking out targets at range. Keep in mind it's damage isn't the best, so use your pistol to take out grunt variants and tough enemies at close range.

This is a personal favorite of mine. Packs a punch, but lower than average ammo. Place your targets. Only hit weak spots of enemies with large health pools. It'll kill a Spitballer in two shots on Hazard 4!
With along with the Neuro Toxin Modification to slow down and poison targets. Crack a Pretorian in
the butt then flank for an easy minigun kill!
Little personal tip from me; you have good accuracy while jumping mid air and not pressing a movement key. Use this fact to allow yourself more mobility and accuracy while getting away from the little buggers!

I'm not doing other overclocks for the Revolver YET because this is focusing on the Minigun loadouts.

The Vampire and Berserker perks are great together. If a lot of grunts start streaming in, start whacking them with your pickaxe!
I also take Elemental Resistance since gunner has to be more of a tank since he is the least mobile of the classes. Elemental damage is always a threat!
Last but certainly not least, Sprint burst perk. This is good on all classes, but ESPECIALLY gunner since he is the least mobile. It's perfect for crossing large gaps and getting out of melee in desperate situations.

The Shield Generator is pretty simple. Use the modifications to increase the duration and radius. But be careful as it has a 12.5 second cooldown (After the deploy duration is over) Make sure you're killing or reviving your allies while inside the bubble!

If the enemy is being funneled well you can toss a grenade in their face for massive AoE damage. And you have 6 Sticky Grenades! Incendiary Grenades are great for covering choke points and Cluster Grenades are perfect for carpet bombing a wide area quickly.

Faster Armor regen delay is good. There's no negative factor for taking it. Regen rate isn't a great idea, as long as you get out of combat you can let it regenerate before reentering combat.
Taking more health over armor is great for staying power in tense situations, especially on Salvage missions. Another modification for tense situations is the extended breathing period when being revived. Let's face it, being the least mobile class in the game you're likely to be caught and dog piled on by Glyphids. When that Scout with instant revive comes in to revive you, start blasting for a short time before putting up your shield and holding the area for your team!

So that's it! That's all you need to know to have Hazard 5 ready Heavy Gunner Minigun loadouts!
I'll add Autocannon when I find the best meta loadouts for it. But so far I love the DAKKA of the Minigun!
Try out any loadout you like! Please comment below if you notice any faults or alternate modifications you choose! I'm happy to discuss anything you're wondering about!

Cheers, Rock and Stone Brothers!