4l80e?

I have a 95 2500 Suburban w/ the 454 and 4l80e trans. My question is that the trans does not lock up in OD unless i'm going downhill and I hit the gas and let off - but as soon as I touch the gas it comes out of lock. RPM at 70 is 21-2200RPM when I get it locked it goes to 16-1700RPM with 265/75/r16 tires. To me this 454 with full torque at 1700RPM should be able to lock up in OD and cruise all day with a dry truck. My 97 tahoe 350 locks-up and holds most any hill at 70 - I know it weights less but it also doesn't have a 4:10 rear.

Any suggestions appriciated - I know I'm a new member but I just bought the truck 2 weeks ago.

Thanks

Tom