97 vortec 5.7 question???

Got 350 vortec and changed oil for first time myself other day. I used 4 quarts of Pennzoil 5w 30 and added a quart of SLICK 50. Was wondering if this was a good idea or not?? Also I have 136,000 and a little miss at idle. Was wondering if there are any easy inexpensive tips to get her running better or idling better??? I have never replaced cap, rotor, plugs or wires. Is this necessary or not? Truck runs great but i wish it would idle better. Thanks for any tips.

I would do a tune up using all GM or Delphi parts, rotor, cap, wires and AC Delco spark plugs. Clean throttle body. Chances are that will take care of the miss you have. Is the CEL coming on? IF so go to autozone and get the codes read and post (they read the codes free of charge). When was the air filter changed last?

Goo Luck