2005 Chevy Silverado cost of repair

Engine Mechanical problem
2005 Chevy Silverado V8 Automatic 105, 00 miles

for tailor res wires, iridium plug, oxygen sensor, renew intake manifold. Cost of repair is $1520.48. Is this reasonable? Is this the same as the 100k tune up?
labor cost including diagnostic $603.26
parts were $796.86
hazmat 38.45
tax 65.97
discount battery not needed $120.00
Total $1520.48

the truck idoled roughly at stop lights so they replaced the battery saying the battery was not getting enough power. This did not solve problem. They did not charge me for the battery now but did charge me for $89.28 for a diagnostic fee on the "tune up". Should'nt they have done this the first time?

Thank you for your time.