need help with 2.8

[greasemonkey321]

put a fully charged battery in it and itll fire right up idle for 20 minutes fine. Shut her off and its very slow to crank.. Replaced the alternator, voltage reg., good battery, new cables, good gronds, had starter tested and its good. when its slow to crank the battery is showing 12.76 volts, jump the solenoid and it dips to about 10.5. I am using a multi meter. now heres the weird thing, I can jump the solenoid with key in the off position and cranks fine, but if i move the key to the run position its slow to crank. just bought the truck and ran great when I got it. Any help appreciated

 

[hende]

starter is on its way out

 

[greasemonkey321]

starter proved good in the tgest though. if i try to drive it ill get about an 8th of a then itll die im almost positive the 2 are related mile