Transmission Issues?

[Bowtie_Beast]

Had a crazy thing happen the other day on the way to work. Transmission didn't want to shift into 3rd gear. It felt like it came out of second and the just revved like it was in neutral. I let up on the accelerator and got on it again and it was in third. It did this three times and then fourth time it wasn't there so I dropped it into 3 and it went in. 
I do bookkeeping in the morning at a repair shop so I dropped it off. A tech took it for a ride later in the day and it shifted fine. He said it was a little low on trans fluid and put in about a quart. Drove it today and it seemed fine. IDK.? 
Any thoughts? It's a 2004 XL Denali with 269,000. I'm hoping it will make it till spring when I get my bonus so I can sell it and get something else.

[sefiroxx]

Had a crazy thing happen the other day on the way to work. Transmission didn't want to shift into 3rd gear. It felt like it came out of second and the just revved like it was in neutral. I let up on the accelerator and got on it again and it was in third. It did this three times and then fourth time it wasn't there so I dropped it into 3 and it went in. 
I do bookkeeping in the morning at a repair shop so I dropped it off. A tech took it for a ride later in the day and it shifted fine. He said it was a little low on trans fluid and put in about a quart. Drove it today and it seemed fine. IDK.? 
Any thoughts? It's a 2004 XL Denali with 269,000. I'm hoping it will make it till spring when I get my bonus so I can sell it and get something else.

This gen of transmissions typically need high pressure to hold in 3rd and 4th. If low on fluid, it may not engage or slip. Suggest changing the fluid as you might have burned the clutches a bit.

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[Hubert Lambert]

Got a 99 GMC 5.3 trans is in limp mode code for shift solinod electrical how does that just happen when i pulled up to work it was fine the after my shift it was like that the crank sensor is going out also could that have something to do with it.