If the transmission goes to shift into 3rd gear and just neutrals, it is an internal problem not a solenoid. With a no 3rd or 4th gear complaint I would bet that you have lost what is referred to as the 3-4 clutch. HTH Vince
my 4l60e in third gear loses acceleration but it doesnt drop into like a neutral but no matter how hard i press the pedal unless i stomp on it it hardly gains rpms. Even when i stomp on it it hardly gains speed.
Most people describe a completely worn out 3-4 clutch as a shift into Neutral, just banging the rev limiter. If it stays in 2nd gear, that indicates the WOT shift table (in the tune) has too high a MPH to make a shift. This could be caused by slippage in the converter, slippage in the trans, or if the tune was just changed - a bad tune. It commonly happens after a higher stall converter is installed.
Was anything changed recently? Is the car stock?
If nothing was changed and the car is stock, it could be a slipping band while in 2nd gear.