simple really. they just pick it up, type in your password then do what ever they want CAULSE THEY HAVE SIMLY HACKED YOUR PHONE!!!!!!!!!!!!!!!!!!!!!!
I'd run a compression test, you could have a sticking or burned valve. Also, if that doesn't show any problems, check the timing and the ignition advance. When you pulled the plugs were any of them fouled or did any look different? The insulators should all be light tan in color, not bright white and not black. Plugs give you a lot of valuable information when you change them. White plugs mean that a cylinder is running too lean, it can result in burned valves or a damaged piston. Black plugs indicate either a rich burn condition, oil fouling or possibly a weak spark. Wet plugs indicate extreme oil fouling or possibly flooding. A compression test is valuable, especially when performing a tune-up on an older engine. The Chev truck engines of that era were incredibly tough and have a good record of reliability, but bad things can happen. Don't forget to mark the plug wires.