Tachometer reving while in gear

Lately, I noticed that while I am driving, if I pump the accerelator, the tachometer will go up and down in a wide range. The truck will jerk as I step on the gas to accerelate but the tachometer reading is now moving like I am in neutral. My transmission fluid level is good but I have not change the fluid filter for the last 80,000 miles. Should I worry?

Sounds like you transmission is slipping.

When you stomp on the gas the truck will not accelerate much by the engine will get faster?

Is that what you are saying?

Have you checked your transmission fluid with the engine running lately?

Sounds like you transmission is slipping.

When you stomp on the gas the truck will not accelerate much by the engine will get faster?

Is that what you are saying?

Have you checked your transmission fluid with the engine running lately?

Thanks for replying, yup, that's what I meant.
I check my transmission fluid and it looks ok. Should I Change the transmission fluid filter? I am planning to tow a big trailer this summer.

You won't be towing anything with the transmission like this.

Sounds like it is slipping badly.

What year is this truck? What type of engine/vin number? Are you getting all gears? Is it shifting alright through all the gears and into overdrive? It sounds like your still driving it. Before giving up on the transmission, depending on what year/type, I'd be checking some simple things first.