Broken Motor Mount Hardware/Brackets

I have broken the hardware securing my motor mounts multiple times. First time was just the passenger side. I ended up buying two new motor mounts, nuts and bolts from toyota, and replaced both sides as a precaution. Two weeks laters I break both sides hardware in the same drive, causing the fan to rub on the shroud. I trailered to a lift and the mounts were still in new condition so I used Grade 8 hardware with a washer on each side and lock-tite. Another week later I break passenger side hardware again, and again replace with grade 8.
I'm driving these bolts on with an air-impact, and from both top and bottom angles I can see the brackets are tightened flush each time.
My question is if anyone else has had a problem with breaking the motor mount hardware multiple times. One of the times I noticed the bolts were loosing up so I tightened them, all other times the head of the bolt is literally shearing off. I switched to Grade 8 after I initially broke the OEM bolts, but they're still breaking.

I'm considering welding the motor mounts to the brackets connecting to the frame. Has anyone had any experience with this issue and/or heard of having to weld the motor mounts due to constantly breaking hardware?

I do live in a canyon so 90% of my driving is off road.

I am open to any advice, thanks in advance.

 

Back in the day chaining them and tack welding was popular. Haven’t heard this issue recently so I’m thinking you’re either using the wrong hardware or have a serious vibration issue. Maybe try some blue loctite.

 

Any idea what could cause excessive vibration?

Trans mount is in good condition.

Other than rotational force of the engine I'm having a hard time thinking what could be causing the bolts to break.

 

A u joint out of tune or possible your harmonic balancer?

 

Your dealing with Stock Horsepower and Torque?

The engine has not been swapped or new frame perches welded in .

Has this happened since New ?? Something not lined up correct when the truck was built.

I never had engine mount issues with High Horse Power engines even doing far to many Hole Shots

Blown differentials twisted drive shafts

Your Hardware Supplier got a lot of counterfeit Grade 8 hardware a thought