Path1, I'm not following what the problem was in the first place.
You already have a fass lift pump ilo the stock lift pump, and it WAS pulling fuel thru the stock pickup out of the tank?
Did you have fuel delivery issues before going to the shop or replacing the sending unit for the fuel guage?
Now your not getting fuel to the IP (inj pump)? Sounds like.....
So had them drop the tank again and install a fass draw straw and still not getting fuel?
If this is all correct, first the shop needs to put a pressure guage on the low side of the ip to make sure it's the LP or lines before the ip. You should see good positive pressure out of the LP. Like 10psi? Idk what the actual numbers are.
If this is all correct to this point, then either there's an air leak on the low pressure side causing the LP to not pull enough fuel or the fass pump is shot.
To the original question, not a mechanic but 5 hrs is too much to drop the tank and replace. If there was other work then maybe not bad.
If your LP is working, they could have just put 12v to it and a hose and pumped the tank dry before dropping, or use 2 jacks and drop it while full. Last choice IMO if you have a 5th hitch etc in the bed would be to pull the bed.
I've just pulled the bed on other trucks as it seemed less risky than dropping a full tank but need multiple people to pull or slide the bed like 12V said above.
Sounds like you need help diagnosing the problem correct?