replaced battery and screen after water damage, phone drops signal

I've recently replaced my water damaged iPhone with a new battery and new front screen assembly.

my phone now continuously drops signal and never achieves LTE which it has in the past. the battery charge also drains drastically fast. down to 20% in less than 3 hours from full charge and all i do is text. Battery used to last up to 2 days.

Phone also shuts down on its own periodically, and when i try to push buttons the apple logo comes on the black screen.

what parts should i look at changing next? or is this sucker a lost cause.

i checked my sim card by putting it into a new iphone and LTE is achieved and no signal is dropped