05 Dodge Neon SRT-4 Slow Crank No Start

05 Neon SRT-4, recently seemingly out of nowhere have a slow crank no start issue with the car. Car is heavily modified higher compression engine 12:0, fresh build but over 1k miles of driving on this build. I cannot recall any other changes when the car was running okay from now aside from switching to a higher oil viscosity from 5w-40 to a 10w-60 now for a bit more oil pressure due to larger rod bearing clearance. Starter on the car had been acting up intermittent the pinion would not come out consistently so I swapped it for another used unit I had around. This starter cranked more consistent but was slow cranking and after a few seconds blows my 200a inline fuse to battery which is trunk mounted. I have a Optima yellow top deep cycle battery there 660cca and its just over a year old always on a charger since new. 0G wire run from car engine bay fuse box to battery and 0G ground to trunk sheet metal factory ground spot in trunk. Also when engine was out I upgraded power to alt with 2G wire feed, power to starter 2G feed and grounded off engine block to rad support with 2G as well as off alt body to head and then head to pass strut tower. The battery when tested using a load tester shows "good" with no load voltage of 13.32V and load voltage of 12.32V state of charge 100% and state of health >90% however when logging during cranking I show voltage drop to zero if not very close to it. I'm going to try another battery tonight that's much higher at 2000cca, aside from that I'm tossing a new starter in and I need to physically remove and clean all grounds yet. any other suggestions or tests would be very appreciated. Thanks!

grounded off engine block to rad support with 2G as well as off alt body to head and then head to pass strut tower

I assume you have a cable from the negative battery post, to the engine block, too?

I have a Optima yellow top deep cycle battery there 660cca ... I'm going to try another battery tonight that's much higher at 2000cca

With all of the mods, a bigger battery would be a good idea.

The battery when tested using a load tester shows "good" with no load voltage of 13.32V

No-load battery voltage should be 12.6 volts. A battery can read more than 12.6 volts because it was just removed from a charger. This is called a "surface charge". Testing a battery that has a surface charge will not have "true" readings. Dissipate the surface charge by allowing the battery to "rest" for a period of time. Or, by inducing a load to the battery. The first load test that you performed would have been good to dissipate the surface charge, but not have accurate readings. If you were to wait a few minutes, then test again, you will have a more accurate results. Passing a load test, but dropping to zero during cranking is odd. Check to ensure that all of the belt pulleys and accessories spin, freely. Maybe, remove the belts, and pull the spark plugs to ensure that the engine, itself, isn't bound.

I actually believe thats what i have been missing a direct ground from block to neg post, i did not install that when i moved batt to trunk. testing the other night with a battery and jumpers clipped one to block and neg post and one on starter post car cranks normally now. Thank you I will deff be adding the ground to neg in read now.