Did the Dealer replace the TCM? Perhaps it was a bad one, replacement parts can be defective at times.
Was the transmission scanned for codes by the local Dodge Dealer before giving a solution?
Did anybody check the wiring? For example, a bad connection at the output sensor can put the transmission into limp mode. The speedometer will not work either in that case. Does your speedometer work when in limp mode?
The transmission goes into limp mode to protect itself from damage, so there should be a fault code available.
2007 GC SXT - Magnesium - S&G - 3.8L - 145,500 kms
2002 GC Sport - Stone White - 3.3L - 328,350 kms
2003 Jeep TJ Sport - 4.0L - 258,980 kms