Our 99' Crown Vic LX is approaching 280k miles on it now, still the original engine and transmission. Oil has been changed every 3k, up to using 10W30 in it now, burns through about two quarts of oil in that time. Trans fluid was every 50k, but as we got over 200k it's been more often than that. It shudders when it's warmer outside, and now that we are getting into spring, it's come back, but worse now then before. Every time I have changed the fluid/filter I put anti-shudder in it each time but I'm wondering if anyone could suggest anything else? Lucas Trans-slip? Although it never has slipped. I have been using Valvoline Mercon V. I love the car and still wax the paint, but with it's age and mileage it's not worth putting a transmission in so when it goes so does the car. Goal was 300k when we got it way back when I'd like to get it there.

Thanks.