Okay then is there any way to add some HP to the TBI?
yes you can make hp with TBI
my suggestion is....get the vehicle running right by doing all the maintenance first. Make sure your drivetrain is stout enough to add the hp. Remember it’s a older truck with higher miles and most likely original drivetrain. So you start adding hp you’ll most likely find out what is the weak link in your drivetrain and as you fix it you’ll stress out other parts until you fix all the weak links.. your block is fine. As long as it’s not cracked it’s actually better as it’s gibe through heat cycles. You ca d9 the typical 383 build roller cam/rockets Edelbrock intake abd bore the TBI get a chip burned and that will give you a bunch of torque and up the hp. You’re not gonna have 400 hp but it should be a nice solid runner. you can akeays swap with a LS
there are engine modifications, heads, intakes, TBI mods. And you can do pretty much every engine trick for a 350 chevy that there is like bore stroke polish. Lots of people don’t like TBI. personally i feel is a great simple reliable fuel injection that works without breaking the bank.
As far as the transmission a drain and fill is fine. I’ve changed the fluid on all my transmissions with drain, filter and fill. Never had a issue.
the plug wires and coil....the factory replacement stuff will be fine. You’re not running a dragster engine. My advice to you..get the truck running right, enjoy a dependable truck you can daily drive