I have a 1999 chevy astro van with a 4L60E transmission also it has 150,000 miles



Back in November I had driven from New york to florida with no problems.



I had been down here a few days and decided to gas up and about a few miles from the gas station the check engine soon light came on. I also noticed it would not shift into third gear.



Being so far from home I did not know what to do. I checked the transmission fluid level and added a quart. (it was only about ½ low)



After about two days the problem seemed to correct itself.



I went back to New York with no problems.



Now I have moved down to florida and the van has been great. This last Friday I went to gas up and once again a few miles down the road, the check engine light came on , along with no shifting into third gear.



Luckily I was only a few miles from home, so once again I added a quart of fluid and went home. The next day I drove to advance auto and they checked the codes.



It returned P0758 2-3 shift solenoid circuit malfunction. He cleared the code and it acted normal/ I must make note that before he cleared the code the van was driving OK.



Now just today was driving around town and the check engine light came on and once again no shift into third gear.



I am not sure how to proceed. Should I replace the solenoid. Do you think the fluid and filter change would fix. I am not sure.



any advice would be greatly appreciated

Clean fluid is a must. A little contamination in the solenoid valve spool can cause it to stick. If the fluid and filter haven't been changed in the last 20-30K miles, it's due. While the pan is off, you might want to remove the solenoid and clean it out, and check the solenoid resistance.