When I try to start the engine it turns over painfully slow. The starter I know is good as I had a spare and it made no difference. The battery is 1 year old and fully charged. The contacts are clean. What can it be?

 

It can be one of the accessory pulley is seized and causes the crank to slow.
Or it could be the fuel injector is stuck open and you are trying to compress liquid which is impossible.

 

No pulley issue. Pull the plugs and it turned over the same, about 25rpm. I let it continue and it slowly started to speed up. I put the plugs back in and it started. I know it's not an electrical issue. Battery is charged and in good condition. Starter is good. Wires/connectors are all clean and secure. I hear a squeak when it turns over slowly and once started it is quiet. Very odd situation. Any thoughts?

 

Could it have been starved of oil and seized? Only a guess.
Before you removed the spark plugs, I thought maybe it is the compression cycle which is preventing the crank.
But, you took out the plugs and still had the same slow crank. Could it be one of the bearings preventing the engine from freely cranking?

 

This is an interesting problem..I pull the plugs and turn it over. It turns slow (25rpm) and after 25 seconds the motor turns at a normal rpm. I put the plugs back in and start the engine and it purrs. I shut it on and off and it operates normally. I let it sit for the night and the same thing happens.