Help with trans issue
 

Hi guys and gals,
I need some advice on my 5 speed 84 4x4 truck. I bought it a while back and all was fine. We decided to do a major service including the trans oil. All was fine prior to the oil change mind you. We put 80/90 Chevron GL5 rated that has no Phosphorous or zinc. This particular blend is a non yellow metal eating oil im told. All was great until some 2500 miles later when when it was hot only I couldent shift into 1st and 2nd was pretty tough. I had the clutch and shift tower bushings replaced as it felt like it was hanging and causing the problem. No difference, although it was in need of the clutch anyhow. So.. drained out the Chevron and filled with 4 quarts of Redline MT90. What an instant improvement as it shifted silky smooth.......... for another 2500 miles and now its back to almost as hard at times to get into first only, and again only after driven for several miles. Any ideas? what the heck is the right oil to use in this thing?? BTY the truck has about 180K on it.
Thank You all.

Redline MT90 oil is fine. I've been running it for several years with no problems.

You're problem is rather odd. It doesn't sound like it's the clutch master cylinder or slave cylinder since the problem would be occurring all of the time. The synchronizers may need replacing, but that should be done as a last resort.

Have you replaced the shifter seat and bushing yet?