Leaking radiator? Leaking or loose radiator hose?
you got an antifreeze leak
The classic symptoms of a leaking heater core. Replacing the heater core requires removing the complete dash assembly.
Your best bet is to visit a good auto shop (seller of antifreeze), and say "I want to buy enough antifreeze for a 1990 Chevy 5.7 truck".
The green color antifreeze will be just fine.
you sell it and buy a Chevy truck
if it is leaking from the radiator you can crack an egg and put it in the radiator and it will solve your problem
your truck is likely leaking coolant due to a blown head gasket making white smoke and coolant smell
The heater core is leaking coolant.
That is very possible. You will need to pin point the source of the leak then re-post the results for us to help you further.