I have an 86 Chevy K10 4x4with a 3 spd manual. Its developed a very noticeable shudder when I shift it into 3rd, especially at lower RPMs. There's also a slight shudder in second. The engine runs fine in neutral or coasting. No shudder in first gear. Anyone know what could cause this?

 

maybe the torque converter..try unplugging the connector on the side of the tranny and see if she goes away