In the past 3 days I have changed the spark plugs & wires, had a transmission flush and change and an oil change. yet when I get on the highway I lose speed at 65-70 after a few minutes, the car does not respond when I step on the gas, it just starts slowing down and then suddenly when speed up for a bit and then loses power all over?
Any suggesstions or has anyone run into this problem. BTW it's a GL w/ 2.0 L

sounds like it's fuel starved - how old is the fuel filter?

id check the main cat.

Try running it on the highway for a couple of days at 70mph and see if that helps. Mine had the same problem and that solved it for me.