new to forum 2000 silverado

Got a 2000 Silverado Z71 short box regular cab dark blue with the 4.8. It has a lot of miles 215,000+ but seems to be doing good. Got a great deal on it and it and I needed a truck.

Issues,
-It shifts clunky but nothing outragous for the miles. Added some Lucas tras treatment with little results.
-The tow/overdrive off button on the shifter no longer works.
-It doesn't like to start on cold days. It turns over freely but doesn't want to start. During warm weather it starts perfectly. Battery checked out ok at autozone.

work done,
- new plugs and wires
- all fluids changed to include
- oil every 3,00 miles
- transmission flush
- both differential fluid change
- coolant flush
- Intake cleaning service at local lube shop
- I cleaned out the throttle body with cleaner and a toothbrush

Plans,
- Volant CAI
- Magnaflow dual exhast
- Predator tuner
- fix current issues


I also own a 2006 GTO. It is a fair weather toy/DD. I have a PCV catch can, Billet performance shifter, Predator tuner and some other little mods like blacking out the Pontiac emblems and Royal Purple in trans and dif.