Which antenna are you running? The Travl'er? If so, you probably had the older SK3005 antenna on your previous coach and your newer coach has the SK-SWM3. The dishes are identical in physical size, reception would be the same.
IF you're referring to the SL3 (SWM 3-LNB) versus the SL5 (SWM 5-LNB) then there is no physical difference between the dishes with the exception of which satellites each one will receive. Both dishes receive DirecTV programming on the 99, 101, 103, The SL5 adds only 110 and 119. The 110 has nothing but test channels on it now and the 119 is used for both spot beaming some locals in midsize markets and all the Spanish channels. I'm assuming you do not have the International programming so we don't need to discuss the 95 satellite. All sports programming is found on the 101.
As far as determing whether or not your current sat dish is "bad" it would require a signal detection meter, such as one of the Birddog's or some other similar type digital signal meter to determine signal strengths and aiming. It is also possible the arm holding the LNBs may have been bent, loose or twisted in some manner resulting in a lower signal.
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified